0001564590-20-053540 | 10-Q | XBRL Viewer

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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2020	Nov. 11, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Registrant Name	VAXCYTE, INC.
Entity Central Index Key	0001649094
Current Fiscal Year End Date	--12-31
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity File Number	001-39323
Entity Tax Identification Number	46-4233385
Entity Address, Address Line One	353 Hatch Drive
Entity Address, City or Town	Foster City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94404
City Area Code	650
Local Phone Number	837-0111
Document Quarterly Report	true
Document Transition Report	false
Entity Small Business	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		50,949,711
Entity Filer Category	Non-accelerated Filer
Entity Interactive Data Current	Yes
Entity Current Reporting Status	No
Title of 12(b) Security	Common Stock, $0.001 par value per share
Trading Symbol	PCVX
Security Exchange Name	NASDAQ

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 397,048	$ 58,976
Prepaid expenses and other current assets	3,787	2,747
Total current assets	400,835	61,723
Property and equipment, net	2,539	3,391
Other assets	442	584
Total assets	403,816	65,698
Current liabilities:
Accounts payable	10,685	3,376
Accrued compensation	1,490	414
Accrued manufacturing expenses	24,540	5,777
Accrued expenses (including related party accrual of $134 and $15 as of September 30, 2020 and December 31, 2019, respectively)	2,870	1,305
Deferred rent — current portion	27	19
Lease liability — current portion		161
Total current liabilities	39,612	11,052
Deferred rent — long-term portion	1	17
Redeemable convertible preferred stock warrant liability		450
Other liabilities	128	242
Total liabilities	39,741	11,761
Commitments and contingencies (Note 5)
Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock value		160,310
Stockholders' Equity (Deficit)
Preferred stock, $0.001 par value — 10,000,000 and no shares authorized at September 30, 2020 and December 31, 2019, respectively; no shares issued and outstanding at September 30, 2020 and December 31, 2019, respectively
Common stock, $0.001 par value — 500,000,000 and 52,000,000 shares authorized at September 30, 2020 and December 31, 2019, respectively; 50,949,490 and 4,059,909 shares issued and outstanding at September 30, 2020 and December 31, 2019, respectively	54	7
Additional paid-in capital	541,848	2,967
Accumulated deficit	(177,827)	(109,347)
Total stockholders' equity (deficit)	364,075	(106,373)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$ 403,816	65,698
Series A Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock value		24,967
Series B Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock value		55,151
Series C Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock value		$ 80,192

Condensed Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Related party accrual	$ 134	$ 15
Redeemable convertible preferred stock, shares authorized		35,962,362
Redeemable convertible preferred stock, shares issued		20,390,095
Redeemable convertible preferred stock, shares outstanding		20,390,095
Redeemable convertible preferred stock, liquidation value		$ 172,037
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	52,000,000
Common stock, shares issued	50,949,490	4,059,909
Common stock, shares outstanding	50,949,490	4,059,909
Series A Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value	$ 0.001	$ 0.001
Redeemable convertible preferred stock, shares authorized	10,502,804	10,502,804
Redeemable convertible preferred stock, shares issued	0	6,225,719
Redeemable convertible preferred stock, shares outstanding	0	6,225,719
Redeemable convertible preferred stock, liquidation value	$ 0	$ 26,887
Series B Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value	$ 0.001	$ 0.001
Redeemable convertible preferred stock, shares authorized	11,449,515	11,449,515
Redeemable convertible preferred stock, shares issued	0	6,786,896
Redeemable convertible preferred stock, shares outstanding	0	6,786,896
Redeemable convertible preferred stock, liquidation value	$ 0	$ 60,150
Series C Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, par value	$ 0.001	$ 0.001
Redeemable convertible preferred stock, shares authorized	12,545,824	14,010,043
Redeemable convertible preferred stock, shares issued	0	7,377,480
Redeemable convertible preferred stock, shares outstanding	0	7,377,480
Redeemable convertible preferred stock, liquidation value	$ 0	$ 85,000

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating expenses:
Research and development (including related party expenses of $143 and $1,011 for the three months ended September 30, 2020 and 2019, respectively, and $458 and $1,123 for the nine months ended September 30, 2020 and 2019, respectively)	$ 16,410	$ 9,630	$ 58,903	$ 32,225
General and administrative	4,898	2,510	11,225	6,089
Total operating expenses	21,308	12,140	70,128	38,314
Loss from operations	(21,308)	(12,140)	(70,128)	(38,314)
Other income (expense), net:
Interest expense		(9)	(7)	(33)
Interest income	33	120	212	537
Grant income	787	54	2,152	54
Foreign currency transaction losses	(530)	(186)	(709)	(417)
Change in fair value of the redeemable convertible preferred stock tranche liability		844		2,520
Total other income (expense), net	290	823	1,648	2,661
Net loss and comprehensive loss	$ (21,018)	$ (11,317)	$ (68,480)	$ (35,653)
Net loss per share, basic and diluted	$ (0.41)	$ (2.93)	$ (3.06)	$ (9.54)
Weighted-average shares outstanding, basic and diluted	50,895,358	3,857,298	22,354,212	3,737,779

Condensed Statements of Operations and Comprehensive Loss (Parenthetical) (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Research and development expense to related party	$ 143	$ 1,011	$ 458	$ 1,123

Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock	Series C Redeemable Convertible Preferred Stock	Series D Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ (57,728)					$ 6	$ 1,339	$ (59,073)
Beginning balance, shares at Dec. 31, 2018		6,225,719	6,786,896	3,688,740
Beginning balance at Dec. 31, 2018		$ 24,967	$ 55,151	$ 37,692
Beginning balance, shares at Dec. 31, 2018						3,757,403
Vesting of early exercised stock options	20						20
Stock-based compensation expense	266						266
Net loss	(13,671)							(13,671)
Ending balance at Mar. 31, 2019	(71,113)					$ 6	1,625	(72,744)
Ending balance, shares at Mar. 31, 2019		6,225,719	6,786,896	3,688,740
Ending balance at Mar. 31, 2019		$ 24,967	$ 55,151	$ 37,692
Ending balance, shares at Mar. 31, 2019						3,757,403
Beginning balance at Dec. 31, 2018	$ (57,728)					$ 6	1,339	(59,073)
Beginning balance, shares at Dec. 31, 2018		6,225,719	6,786,896	3,688,740
Beginning balance at Dec. 31, 2018		$ 24,967	$ 55,151	$ 37,692
Beginning balance, shares at Dec. 31, 2018						3,757,403
Exercise of stock options (in shares)	280,836
Net loss	$ (35,653)
Ending balance at Sep. 30, 2019	(92,160)					$ 7	2,559	(94,726)
Ending balance, shares at Sep. 30, 2019		6,225,719	6,786,896	3,688,740
Ending balance at Sep. 30, 2019		$ 24,967	$ 55,151	$ 37,692
Ending balance, shares at Sep. 30, 2019						4,038,239
Beginning balance at Mar. 31, 2019	(71,113)					$ 6	1,625	(72,744)
Beginning balance, shares at Mar. 31, 2019		6,225,719	6,786,896	3,688,740
Beginning balance at Mar. 31, 2019		$ 24,967	$ 55,151	$ 37,692
Beginning balance, shares at Mar. 31, 2019						3,757,403
Exercise of stock options	2						2
Exercise of stock options (in shares)						889
Vesting of early exercised stock options	20						20
Stock-based compensation expense	278						278
Net loss	(10,665)							(10,665)
Ending balance at Jun. 30, 2019	(81,478)					$ 6	1,925	(83,409)
Ending balance, shares at Jun. 30, 2019		6,225,719	6,786,896	3,688,740
Ending balance at Jun. 30, 2019		$ 24,967	$ 55,151	$ 37,692
Ending balance, shares at Jun. 30, 2019						3,758,292
Exercise of stock options	$ 314					$ 1	313
Exercise of stock options (in shares)	279,947					220,671
Issuance of common stock related to early exercised stock options						59,276
Vesting of early exercised stock options	$ 55						55
Stock-based compensation expense	266						266
Net loss	(11,317)							(11,317)
Ending balance at Sep. 30, 2019	(92,160)					$ 7	2,559	(94,726)
Ending balance, shares at Sep. 30, 2019		6,225,719	6,786,896	3,688,740
Ending balance at Sep. 30, 2019		$ 24,967	$ 55,151	$ 37,692
Ending balance, shares at Sep. 30, 2019						4,038,239
Beginning balance at Dec. 31, 2019	$ (106,373)					$ 7	2,967	(109,347)
Beginning balance, shares at Dec. 31, 2019	20,390,095	6,225,719	6,786,896	7,377,480
Beginning balance at Dec. 31, 2019	$ 160,310	$ 24,967	$ 55,151	$ 80,192
Beginning balance, shares at Dec. 31, 2019						4,059,909
Exercise of stock options	49						49
Exercise of stock options (in shares)						28,837
Issuance of common stock related to early exercised stock options						14,819
Vesting of early exercised stock options	128						128
Issuance of preferred stock					$ 109,875
Issuance of preferred stock, net of issuance cost (in shares)					8,220,242
Stock-based compensation expense	372						372
Net loss	(27,142)							(27,142)
Ending balance at Mar. 31, 2020	(132,966)					$ 7	3,516	(136,489)
Ending balance, shares at Mar. 31, 2020		6,225,719	6,786,896	7,377,480	8,220,242
Ending balance at Mar. 31, 2020		$ 24,967	$ 55,151	$ 80,192	$ 109,875
Ending balance, shares at Mar. 31, 2020						4,103,565
Beginning balance at Dec. 31, 2019	$ (106,373)					$ 7	2,967	(109,347)
Beginning balance, shares at Dec. 31, 2019	20,390,095	6,225,719	6,786,896	7,377,480
Beginning balance at Dec. 31, 2019	$ 160,310	$ 24,967	$ 55,151	$ 80,192
Beginning balance, shares at Dec. 31, 2019						4,059,909
Exercise of stock options (in shares)	263,626
Net loss	$ (68,480)
Ending balance at Sep. 30, 2020	364,075					$ 54	541,848	(177,827)
Ending balance, shares at Sep. 30, 2020		0	0	0
Ending balance, shares at Sep. 30, 2020						50,949,490
Beginning balance at Mar. 31, 2020	(132,966)					$ 7	3,516	(136,489)
Beginning balance, shares at Mar. 31, 2020		6,225,719	6,786,896	7,377,480	8,220,242
Beginning balance at Mar. 31, 2020		$ 24,967	$ 55,151	$ 80,192	$ 109,875
Beginning balance, shares at Mar. 31, 2020						4,103,565
Conversion of preferred stock	270,190	$ (24,967)	$ (55,151)	$ (80,192)	$ (109,879)	$ 29	270,161
Conversion of preferred stock (in shares)		(6,225,719)	(6,786,896)	(7,377,480)	(8,220,242)
Conversion of preferred stock (in shares)						28,610,337
Conversion of common stock warrant						30,278
Conversion of preferred stock warrant						16,591
Warrant liability write-off	629						629
Issuance of common stock upon initial public offering, net of issuance costs of $3,296	264,079					$ 18	264,061
Issuance of common stock upon initial public offering, net of issuance cost (in shares)						17,968,750
Exercise of stock options	297						297
Exercise of stock options (in shares)						152,177
Vesting of early exercised stock options	12						12
Issuance of preferred stock					$ 4
Issuance costs for initial public offering						$ (3,296)
Stock-based compensation expense	1,289						1,289
Net loss	(20,320)							(20,320)
Ending balance at Jun. 30, 2020	383,210					$ 54	539,965	(156,809)
Ending balance, shares at Jun. 30, 2020						50,881,698
Exercise of stock options	$ 108						108
Exercise of stock options (in shares)	67,792					67,792
Vesting of early exercised stock options	$ 9						9
Issuance costs for initial public offering	(72)						(72)
Stock-based compensation expense	1,838						1,838
Net loss	(21,018)							(21,018)
Ending balance at Sep. 30, 2020	$ 364,075					$ 54	$ 541,848	$ (177,827)
Ending balance, shares at Sep. 30, 2020		0	0	0
Ending balance, shares at Sep. 30, 2020						50,949,490

Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($)
Series D Redeemable Convertible Preferred Stock
Temporary equity, Issuance costs	$ 125

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (68,480)	$ (35,653)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,073	900
Stock-based compensation expense	3,499	810
Change in fair value of redeemable convertible preferred stock warrant	179	(12)
Change in fair value of redeemable convertible preferred stock tranche liabilities		(2,520)
Loss on disposal of assets	32	1
Asset impairment charges	267
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,040)	(1,071)
Other assets	33	10
Accounts payable	7,330	(1,190)
Accrued compensation	1,076	(283)
Accrued manufacturing expenses	18,763	4,585
Accrued expenses	1,416	1,605
Deferred rent and other long-term liabilities	(8)	79
Net cash used in operating activities	(35,860)	(32,739)
Cash flows from investing activities:
Purchases of property and equipment	(433)	(242)
Proceeds from sale of property and equipment	50
Net cash used in investing activities	(383)	(242)
Cash flows from financing activities:
Payments of capital lease obligations	(61)	(220)
Proceeds from initial public offering, net of underwriters' commissions and discounts	267,375
Payment of issuance costs for initial public offering	(3,368)
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	109,879
Proceeds from exercise of common stock options	454	315
Proceeds from issuance of common stock related to early exercised stock options	36	120
Net cash provided by (used in) financing activities	374,315	215
Net increase (decrease) in cash and cash equivalents	338,072	(32,766)
Cash and cash equivalents, beginning of period	58,976	66,090
Cash and cash equivalents, end of period	397,048	33,324
Supplemental disclosure of cash flow information:
Cash paid for interest	7	33
Supplemental disclosures of non-cash investing and financing activities:
Purchases of property and equipment recorded in accounts payable and accrued expenses	149	197
Conversion of convertible preferred stock into common stock	270,190
Issuance costs for initial public offering included in accounts payable and accrued expenses	$ 17	$ 602

Company Organization and Nature of Business

9 Months Ended

Sep. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Company Organization and Nature of Business

1. Company Organization and Nature of Business

Vaxcyte, Inc. (“we”, “us”, “the Company”, or “Vaxcyte”), headquartered in Foster City, California, was incorporated in the state of Delaware on November 27, 2013 as SutroVax, Inc. and we changed our name to Vaxcyte, Inc. in May 2020. We are a next-generation vaccine company seeking to improve global health by developing superior and novel vaccines designed to prevent some of the most common and deadly infectious diseases worldwide. Our cell-free protein synthesis platform enables us to design and produce optimized protein carriers and antigens, the critical building blocks of vaccines, in ways that are beyond the reach of conventional technology. Our pipeline includes the most broad-spectrum pneumococcal conjugate vaccine (“PCV”) candidates that we believe are currently in development, targeting the $7 billion global pneumococcal vaccine market. Our lead vaccine candidate, VAX-24, is a 24-valent investigational PCV that we expect to advance into clinical trials in the second half of 2021. Our primary activities since incorporation have been to perform research and development, undertake preclinical studies and enable manufacturing activities in support of our product development efforts, organize and staff the Company, plan for the business and establish our intellectual property portfolio, and raise capital to support and expand such activities.

Reverse Stock Split

On June 5, 2020, we filed a certificate of amendment to our amended and restated certificate of incorporation to effect a one-for-1.6870 reverse stock split of our issued and outstanding common stock, preferred stock, stock options and warrants effective on June 5, 2020. Accordingly, all share and per share amounts for all periods presented in the accompanying financial statements and notes thereto have been retroactively adjusted.

Initial Public Offering

In June 2020, we completed an initial public offering (“IPO”) in which we issued and sold 17,968,750 shares of common stock, including shares issued upon the exercise in full of the underwriters’ option to purchase 2,343,750 additional shares of common stock, at a public offering price of $16.00 per share. We received $264.0 million in net proceeds, after deducting underwriting discounts and commissions of $20.1 million and offering expenses of $3.4 million.

Immediately prior to the completion of our IPO, all outstanding shares of redeemable convertible preferred stock were converted into 28,610,337 shares of common stock. Subsequent to the completion of the IPO, there were no shares of redeemable convertible preferred stock outstanding.

Basis of Presentation and Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2020

Accounting Policies [Abstract]

Basis of Presentation and Summary of Significant Accounting Policies

2. Basis of Presentation and Summary of Significant Accounting Policies

Basis of Presentation

These condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted in accordance with such rules and regulations. Certain changes in presentation were made in the condensed balance sheet as of December 31, 2019 to conform to the presentation of the condensed balance sheet as of September 30, 2020.

Unaudited Interim Condensed Financial Statements

The condensed balance sheet as of September 30, 2020, the condensed statements of operations and comprehensive loss, redeemable convertible preferred stock and stockholders’ equity (deficit) for the three and nine months ended September 30, 2020 and 2019, and the condensed statements of cash flows for the nine months ended September 30, 2020 and 2019, are unaudited. The unaudited interim condensed financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of our financial information. The financial data disclosed in the footnotes to the condensed financial statements related to the three and nine months ended September 30, 2020 and 2019 are also unaudited. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any other future annual or interim period. These interim condensed financial statements should be read in conjunction with our audited annual financial statements included in the prospectus dated June 11, 2020 that forms a part of our Registration Statements on Form S-1 (File Nos. 333-238630 and 333-239110) as filed with the SEC pursuant to Rule 424(b)(4) and Rule 462(b) promulgated under the Securities Act of 1933, as amended.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities at the date of the financial statements. On an ongoing basis, we evaluate our estimates and assumptions, including those related to stock-based compensation expense, accruals for certain research and development costs, the valuation of deferred tax assets and income taxes. Management bases our estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates.

Net Loss Per Share

Basic net loss per share is calculated by dividing the net loss by the weighted-average of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.

Deferred Offering Costs

Deferred offering costs consist of fees and expenses incurred in connection with the sale of our common stock in the IPO, including legal, accounting, printing and other IPO-related costs. Prior to the completion of our IPO, deferred offering costs were included in Other assets on the condensed balance sheet. In connection with and as of the closing of our IPO, these costs were reclassified to Additional paid-in capital, representing a reduction to the IPO proceeds. As of September 30, 2020, $3.4 million of these IPO-related costs are included in the Additional paid-in capital line item on the condensed balance sheet. As of December 31, 2019, $1.1 million of deferred offering costs were included in Other assets on the balance sheet.

Concentration of Credit Risk and Other Risks and Uncertainties

Financial instruments that potentially subject us to a concentration of credit risk consist primarily of cash and cash equivalents. We currently invest in money market funds. We maintain bank deposits in federally insured financial institutions and these deposits may exceed federally insured limits. We are exposed to credit risk in the event of a default by the financial institutions holding our cash and cash equivalents. We have not experienced any losses on our deposits of cash and cash equivalents.

We are subject to supplier concentration risk from our suppliers. We source our critical raw materials from a sole source supplier, Sutro Biopharma, Inc. (“Sutro Biopharma”). We also use one contract manufacturing organization (“CMO”), Lonza Ltd. (“Lonza”), to handle most of our manufacturing activities. If we were to experience disruptions in raw materials supplied by Sutro Biopharma, or in manufacturing activities at Lonza, we may experience significant delays in our product development timelines and may incur substantial costs to secure alternative sources of raw materials or manufacturing.

Our future results of operations involve a number of other risks and uncertainties. Factors that could affect our future operating results and cause actual results to vary materially from expectations include, but are not limited to, our early stages of clinical vaccine development; our ability to advance vaccine candidates into, and successfully complete, clinical trials on the timelines we project; our ability to adequately demonstrate sufficient safety and efficacy of our vaccine candidates; our ability to enroll subjects in our ongoing and future clinical trials; our ability to successfully manufacture and supply our vaccine candidates for clinical trials; our ability to obtain additional capital to finance our operations; our ability to obtain, maintain and protect our intellectual property rights; developments relating to our competitors and our industry, including competing vaccine candidates; general and market conditions; and other risks and uncertainties, including those more fully described in the “Risk Factors” section of this Quarterly Report on Form 10-Q.

Recently Adopted Accounting Pronouncements

In June 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting, which simplifies the accounting for share-based payments granted to non-employees for goods and services. This standard expands the scope of Topic 718, Compensation-Stock Compensation, to include share-based payments issued to non-employees for goods and services. Consequently, the accounting for share-based payments to non-employees and employees was substantially aligned. The ASU supersedes Subtopic 505-50, Equity—Equity-Based Payments to Non-Employees. This standard is effective for fiscal years beginning after December 15, 2019 and interim periods within fiscal years beginning after December 15, 2020. The standard should be adopted on a modified retrospective basis which recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We adopted this ASU as of January 1, 2020. The adoption of this ASU had no material impact on our financial statements or disclosures.

Recently Issued Accounting Pronouncements—Not Yet Adopted

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASU 2016-02 was subsequently amended by ASU 2018-01, ASU 2018-10, ASU 2018-11, ASU 2018-20, ASU 2019-01, ASU 2019-10 and ASU 2020-05, which the FASB issued in January 2018, July 2018, July 2018, December 2018, March 2019, November 2019 and June 2020, respectively (collectively, the “amended ASU 2016-02”). The amended ASU 2016-02 requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. The new standard establishes a right-of-use (“ROU”) model that requires a lessee to recognize a ROU asset and a lease liability on the balance sheet for all leases with a term longer than 12 months. Under the new standard, leases will be classified as either finance leases or operating leases, with classification affecting the pattern and classification of expense recognition in the income statement.

The new standard is effective for us on January 1, 2022, with early adoption permitted. We expect to adopt the new standard on the effective date. The new standard requires an entity to adopt using one of two approaches, either (i) retrospectively to each prior reporting period presented in the financial statements with the cumulative effect recognized at the beginning of the earliest comparative period presented, or (ii) retrospectively at the beginning of the period of adoption through a cumulative-effect adjustment. Although we are currently evaluating the impact of adoption on our financial statements and related disclosures, we believe the most significant changes will be the recognition of the ROU assets and the related lease liabilities for our operating leases on our condensed balance sheets.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740). The amendments in ASU 2019-12 simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify U.S. GAAP or other areas of Topic 740 by clarifying and amending existing guidance. The new standard is effective for us on January 1, 2022 and for interim periods beginning on January 1, 2023. We are currently evaluating the impact that the standard will have on our condensed financial statements and related disclosures.

Fair Value Measurements and Fair Value of Financial Instruments

9 Months Ended

Sep. 30, 2020

Fair Value Disclosures [Abstract]

Fair Value Measurements and Fair Value of Financial Instruments

3. Fair Value Measurements and Fair Value of Financial Instruments

Assets and liabilities recorded at fair value on a recurring basis in the condensed balance sheets, as well as assets and liabilities measured at fair value on a non-recurring basis or disclosed at fair value, are categorized based upon the level of judgment associated with inputs used to measure their fair values. The accounting guidance for fair value provides a framework for measuring fair value and requires certain disclosures about how fair value is determined. Fair value is defined as the price that would be received upon the sale of an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance also establishes a three-level valuation hierarchy that prioritizes the inputs to valuation techniques used to measure fair value based upon whether such inputs are observable or unobservable. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect market assumptions made by the reporting entity. The three-level hierarchy for the inputs to valuation techniques is briefly summarized as follows:

Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;

Level 2—Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and

Level 3—Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.

Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. Our assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. Changes in the ability to observe valuation inputs may result in a reclassification of levels of certain securities within the fair value hierarchy. We recognize transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs.

Level 1 securities consist of highly liquid money market funds for which the carrying amounts approximate their fair values due to their short maturities. Level 3 liabilities that are measured at fair value on a recurring basis include the redeemable convertible preferred stock warrant. The redeemable convertible preferred stock warrant was measured using an option pricing method by estimating the value using the Black-Scholes model. The inputs used in the Black-Scholes model included the value of the redeemable convertible preferred stock, the risk-free interest rate, the expected term of the instrument and the expected volatility. There was no outstanding redeemable convertible preferred stock warrant as of September 30, 2020. Below are inputs used for the Level 3 liability as of December 31, 2019:

	December 31, 2019
	Redeemable Convertible Preferred Stock Warrant
Value of Series C Redeemable Preferred Stock Per Share	$	6.82
Risk-Free Rate		1.90	%
Volatility		73.5	%
Term in Years	8.42

During the periods presented, we have not changed the manner in which we value liabilities that are measured at estimated fair value using Level 3 inputs. There were no transfers within the hierarchy during the three or nine months ended September 30, 2020 or the year ended December 31, 2019.

The following tables set forth our financial instruments measured at fair value on a recurring basis by level within the fair value hierarchy at September 30, 2020 and December 31, 2019:

	September 30, 2020
	Total		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds ⁽¹⁾	$	392,272	$	392,272	$	—	$	—

	December 31, 2019
	Total Fair Value		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds ⁽¹⁾	$	48,168	$	48,168	$	—	$	—
Liabilities:
Redeemable convertible preferred stock warrant liability	$	450	$	—	$	—	$	450

(1)	Included within cash and cash equivalents on the condensed balance sheet.

The following table provides a summary of changes in the estimated fair value of our Level 3 financial instrument, which was written off upon our IPO in June 2020. No new warrant liabilities were issued during the three months ended September 30, 2020:

	Warrant Liability
	(in thousands)
Balance — December 31, 2019	$	450
Change in fair value		179
Balance — March 31, 2020		629
Warrant liability write-off upon IPO		(629	)
Balance — June 30, 2020	$	—

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Balance Sheet Details

9 Months Ended

Sep. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Balance Sheet Details

4. Balance Sheet Details

Property and Equipment, Net

Property and equipment, net as of September 30, 2020 and December 31, 2019 consisted of the following:

	September 30,			December 31,
	2020			2019
	(in thousands)
Furniture and equipment	$	397		$	397
Computers and computer software		169			146
Lab equipment		3,887			3,260
Leasehold improvements		1,903			1,884
Capital leases — lab equipment		—			686
Construction in Progress		14			—
Total property and equipment		6,370			6,373
Less: accumulated depreciation and amortization		(3,831	)		(2,982	)
Property and equipment, net	$	2,539		$	3,391

Depreciation and amortization expense for the three months ended September 30, 2020 and 2019 was $0.3 million and $0.3 million, respectively, of which $0 and $0.1 million related to capital lease amortization expense for the three months ended September 30, 2020 and 2019, respectively. Depreciation and amortization expense for the nine months ended September 30, 2020 and 2019 was $1.1 million and $0.9 million, respectively, of which less than $0.1 million and $0.2 million related to capital lease amortization expense for the nine months ended September 30, 2020 and 2019, respectively.

Accrued Expenses

Accrued expenses as of September 30, 2020 and December 31, 2019 consisted of the following:

	September 30,		December 31,
	2020		2019
	(in thousands)
Preclinical studies	$	1,969	$	844
Professional fees		486		397
Other accrued expenses		415		64
Total	$	2,870	$	1,305

Commitments and Contingencies

9 Months Ended

Sep. 30, 2020

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

5. Commitments and Contingencies

Capital Leases

We entered into several capital lease obligations for lab equipment during 2016 and 2017. The terms of the leases were 36 months with interest rates ranging from 6.9% to 15.0%. Interest expense for the three and nine months ended September 30, 2020 and 2019 was immaterial.

The present value of the annual rental payments, including guaranteed residual value, was equal to 90% of the fair market value of the assets at the lease inception dates. The underlying assets and related amortization were included in the appropriate fixed asset category and related depreciation account, respectively.

In October 2019 and March 2020, we entered into lease buyout agreements for two pieces of lab equipment. The remaining balances of the capital lease assets for these two pieces of equipment were transferred from Capital leases — lab equipment to Lab equipment at the time of the lease buyouts (See Note 4, “Property and Equipment, Net”). The remaining capital leases had bargain purchase options and we purchased the equipment related to these leases in June 2019 and March 2020 when the leases ended. As of September 30, 2020, there was no remaining balance of lease liability on the balance sheet and there were no future minimum payments required under capital leases.

Property and equipment, net at December 31, 2019 included the following amounts for leases that have been capitalized:

	Useful Life (Years)	December 31, 2019
		(in thousands)
Capital lease equipment	3 - 5	$	686
Less: accumulated amortization			(471	)
		$	215

Operating Leases

In July 2016, we entered into a five-year lease agreement for our headquarters facility located in Foster City, California. The term of the lease is from September 1, 2016 to August 31, 2021, with two 30-month renewal options. In July 2019, we leased another facility in Foster City, California as a result of growth in personnel. The lease term began on July 1, 2019 and ends on October 31, 2021, with no renewal options. Both of the Foster City lease agreements provide for escalations of rent payments each year. We record rent expense for these two leases on a straight-line basis over the terms of the leases and deferred rent based on the difference between rent expenses and cash rental payments. In addition to payment of base rent, we are also required to pay property taxes, insurance and common area expenses for both of the Foster City leases. We also lease an office in San Diego, California with a lease term ending on March 31, 2021. In addition to payment of base rent for the San Diego office lease, we are also required to pay common area expenses. Rent is payable monthly for all facility leases.

Future minimum payments required under operating leases as of September 30, 2020 are as follows:

	(in thousands)
Remainder of 2020	$	183
2021		531
Total future minimum payments	$	714

Rent expense recognized under the leases was $0.2 million and $0.2 million for the three months ended September 30, 2020 and 2019, respectively, and $0.5 million and $0.4 million for the nine months ended September 30, 2020 and 2019, respectively.

Legal Contingencies

From time to time, we may become involved in legal proceedings arising from the ordinary course of business. We record a liability for such matters when it is probable that future losses will be incurred and that such losses can be reasonably estimated. Significant judgment by us is required to determine both probability and the estimated amount. Management is currently not aware of any legal matters that could have a material adverse effect on our financial position, results of operations or cash flows.

Guarantees and Indemnifications

In the normal course of business, we enter into agreements that contain a variety of representations and provide for general indemnification. Our exposure under these agreements is unknown because it involves claims that may be made against us in the future. To date, we have not paid any claims or been required to defend any action related to our indemnification obligations. As of September 30, 2020, we did not have any material indemnification claims that were probable or reasonably possible and consequently have not recorded related liabilities.

Indemnification

To the extent permitted under Delaware law, we have agreed to indemnify our directors and officers for certain events or occurrences while the director or officer is, or was, serving at our request in such capacity. The indemnification period covers all pertinent events and occurrences during the director’s or officer’s service. The maximum potential amount of future payments we could be required to make under these indemnification agreements is not specified in the agreements; however, we have director and officer insurance coverage that reduces our exposure and enables us to recover a portion of any future amounts paid. We believe the estimated fair value of these indemnification agreements in excess of applicable insurance coverage is minimal.

Development and Manufacturing Services Agreement

On October 21, 2016, we entered into a development and manufacturing services agreement with Lonza (the “Lonza DMSA”), pursuant to which Lonza would provide certain process development and manufacturing services and we would pay certain fees according to specified project plans to support our efforts to develop superior, novel conjugate vaccines. In January 2017, July 2017 and September 2017, we entered into amendments to the Lonza DMSA, which significantly expanded the scope of process development and manufacturing work to be provided by Lonza for our lead PCV program. We have the option to cancel signed orders at any time upon written notice, which may or may not be subject to payment of a cancellation fee. The level of cancellation fees is generally dependent on the timing of the written notice in relation to the commencement date of the work, with the maximum cancellation fee equal to the full price of the work order.

In the September 2017 amended agreement, we and Lonza agreed to defer the completion payments for any stage that commences after December 31, 2019 or has not been completed by December 31, 2019 until the earlier of the completion of all Investigational New Drug (“IND”)-enabling activities or December 31, 2020. In March 2020, Lonza orally agreed to defer the completion payments until April 30, 2021.

In June 2018, we and Lonza agreed to certain terms for potential future equity payments as partial satisfaction of future obligations to Lonza. This agreement states that the initial pre-IND cash payments will be subject to a specified dollar cap (the “Initial Cash Cap”). After the Initial Cash Cap has been reached, we have the option to make any further pre-IND payments due to Lonza in cash, equity, or a combination of both, at our election, provided that Lonza may elect to receive up to 25% of pre-IND payments in equity, up to a maximum of $2.5 million and provided that no more than $10 million of pre-IND payments shall be made equity. The Initial Cash Cap had not been reached as of September 30, 2020. As such, no amount has been recorded with respect to the potential future payments above the Initial Cash Cap at September 30, 2020 and December 31, 2019.

Redeemable Convertible Preferred Stock

9 Months Ended

Sep. 30, 2020

Temporary Equity Disclosure [Abstract]

Redeemable Convertible Preferred Stock

6. Redeemable Convertible Preferred Stock

In connection with our IPO in June 2020, the outstanding shares of our Series A, Series B, Series C and Series D Redeemable Convertible Preferred Stock automatically converted into 28,610,337 shares of common stock.

The authorized, issued and outstanding shares of redeemable convertible preferred stock and liquidation preferences as of December 31, 2019 were as follows:

	December 31, 2019
	Shares Authorized		Issued and Outstanding		Original Issuance Price		Carrying Value		Liquidation Preference
							(In thousands)
Series A Redeemable Convertible Preferred		10,502,804		6,225,719	$	4.32	$	24,967	$	26,887
Series B Redeemable Convertible Preferred		11,449,515		6,786,896		8.86		55,151		60,150
Series C Redeemable Convertible Preferred		14,010,043		7,377,480		11.52		80,192		85,000
		35,962,362		20,390,095			$	160,310	$	172,037

In March, 2020, we sold an aggregate of 8,220,242 shares of our Series D redeemable convertible preferred stock at a purchase price of $13.3816 per share for an aggregate purchase price of $110.0 million.

There were no shares of redeemable convertible preferred stock outstanding as of September 30, 2020.

Common Stock

9 Months Ended

Sep. 30, 2020

Equity [Abstract]

Common Stock

7. Common Stock

At September 30, 2020 and December 31, 2019, our certificate of incorporation authorized us to issue up to 500,000,000 and 52,000,000 shares of common stock with $0.001 par value per share, respectively, of which 50,949,490 and 4,059,909 shares were issued and outstanding, respectively. The holders of our common stock are also entitled to receive dividends whenever funds are legally available, when and if declared by our board of directors. As of September 30, 2020 and December 31, 2019, no dividends have been declared. Each share of common stock is entitled to one vote.

At September 30, 2020 and December 31, 2019, we had reserved common stock for future issuances under the 2020 Equity Incentive Plan (the “2020 Plan”) and the 2014 Equity Incentive Plan (the “2014 Plan”), and had issued 66,982 shares outside of the 2014 Plan and 2020 Plan as follows:

	September 30,		December 31,
	2020		2019
Options issued and outstanding		5,094,669		3,364,568
Shares available for future stock option grants		4,839,649		835,941
Conversion of redeemable convertible preferred stock		—		20,390,095
Common stock warrant		—		31,857
Redeemable convertible preferred stock warrant		—		59,276
Total		9,934,318		24,681,737

Warrants

9 Months Ended

Sep. 30, 2020

Equity [Abstract]

Warrants

8. Warrants

In connection with our IPO in June 2020, the common stock warrant and Series C redeemable convertible preferred stock warrant were automatically net exercised for an aggregate 46,869 shares of common stock.

Warrants issued and outstanding as of December 31, 2019 were as follows:

Warrants to Purchase Stock

Number of

Warrants

Issued and

Outstanding

Issue Date

Expiration

Date

Exercise

Price

Common stock

31,857

July 10, 2015

July 10, 2025

0.79

Series C redeemable convertible preferred stock

59,276

May 29, 2018

May 29, 2028

11.52

Total

91,133

Equity Incentive Plans

9 Months Ended

Sep. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Equity Incentive Plans

9. Equity Incentive Plans

2020 and 2014 Equity Incentive Plans

In June 2020, our board of directors adopted, and our stockholders approved, the 2020 Plan, which became effective on June 11, 2020. Under the 2020 Plan, we may grant incentive stock options, non-statutory stock options, appreciation rights, restricted stock and restricted stock units to employees, consultants and directors. A total of 10,150,000 shares of common stock were approved to be initially reserved for issuance under the 2020 Plan. The number of shares that remained available for issuance under the 2014 Plan as of the effective date of the 2020 Plan and shares subject to outstanding awards under the 2014 Plan as of the effective date of the 2020 Plan that are subsequently canceled, forfeited or repurchased by us will be added to the shares reserved under the 2020 Plan. In addition, the number of shares of common stock available for issuance under the 2020 Plan will be automatically increased on the first day of each calendar year during the ten-year term of the 2020 Plan, beginning with January 1, 2021 and ending with January 1, 2030, by an amount equal to 5% of the outstanding number of shares of our common stock on December 31^st of the preceding calendar year or such lesser amount as determined by our board of directors. As of September 30, 2020, an aggregate of 4,839,649 shares of common stock were available for issuance under the 2020 Plan.

Our 2014 Plan permitted the granting of incentive stock options, non-statutory stock options, restricted stock and other stock-based awards. Subsequent to the adoption of the 2020 Plan, no additional equity awards can be made under the 2014 Plan. Shares reserved and remaining available for issuance under the 2014 Plan were added to the 2020 Plan reserve upon its effectiveness. As of September 30, 2020, 4,809,187 shares and 218,500 shares of common stock were subject to outstanding options under the 2014 Plan and 2020 Plan, respectively.

The terms of the 2014 Plan permit the exercise of options granted prior to vesting, subject to required approvals. The unvested shares are subject to our lapsing repurchase right upon termination of employment at the original purchase price. Shares purchased by employees pursuant to the early exercise of stock options are not deemed, for accounting purposes, to be issued until those shares vest according to their respective vesting schedules. Cash received for early exercised stock options is recorded as other liabilities on the condensed balance sheet and is reclassified to common stock and additional paid-in capital as such shares vest.

At September 30, 2020 and December 31, 2019, 22,700 and 86,409 shares, respectively, remained subject to our right of repurchase as a result of the early exercised stock options. The remaining liabilities related to early exercised shares as of September 30, 2020 and December 31, 2019 were less than $0.1 million and $0.2 million, respectively, and were recorded in other liabilities.

Activity under our 2020 Plan and 2014 Plan, which excludes options to purchase 66,982 shares granted outside of the 2020 Plan and 2014 Plan, was as follows:

				Options Outstanding
Stock Option Activity	Options Available for Grant			Number of Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balances — December 31, 2019		835,941			3,297,586		$	1.93
Additional shares authorized		5,997,435			—
Options granted		(2,065,590	)		2,065,590		$	6.57
Options exercised		—			(263,626	)	$	1.86
Options forfeited		71,863			(71,863	)	$	2.47
Balances — September 30, 2020		4,839,649			5,027,687		$	3.83		8.22	$	228,992
Vested and expected to vest — September 30, 2020					5,027,687		$	3.83		8.22	$	228,992
Exercisable at September 30, 2020					1,782,595		$	1.85		6.70	$	84,725

During the three months ended September 30, 2020 and 2019, 67,792 and 279,947 shares of stock options, respectively, were exercised for cash at a weighted-average price per share of $1.60 and $1.55, respectively. The weighted-average grant date fair value of options granted for the three months ended September 30, 2020 and 2019 was $29.83 and $2.31, respectively. The intrinsic value of the stock options exercised was $2.5 million and $0.2 million for the three months ended September 30, 2020 and 2019, respectively.

During the nine months ended September 30, 2020 and 2019, 263,626 and 280,836 shares of stock options, respectively, were exercised for cash at a weighted-average price per share of $1.86 and $1.55, respectively. The weighted-average grant date fair value of options granted for the nine months ended September 30, 2020 and 2019 was $8.17 and $1.51, respectively. The intrinsic value of the stock options exercised was $5.1 million and $0.2 million for the nine months ended September 30, 2020 and 2019, respectively.

2020 Employee Stock Purchase Plan

In June 2020, our board of directors adopted, and our stockholders approved, the 2020 Employee Stock Purchase Plan (the “2020 ESPP”), which became effective on June 11, 2020. The 2020 ESPP permits participants to purchase common stock through payroll deductions of up to 15% of their eligible compensation. A total of 650,000 shares of common stock were approved to be initially reserved for issuance under the 2020 ESPP. In addition, the number of shares of common stock available for issuance under the 2020 ESPP will be automatically increased on the first day of each calendar year during the ten-year term of the 2020 Plan, beginning with January 1, 2021 and ending with January 1, 2030, by an amount of 1% of the outstanding number of shares of our common stock on December 31^st of the preceding calendar year or such lesser amount as determined by our board of directors. As of September 30, 2020, 650,000 shares of common stock were available for issuance under the 2020 ESPP.

Stock-based Compensation

We estimated the fair value of employee stock options using the Black-Scholes option-pricing model for the three and nine months ended September 30, 2020 and 2019 using the following weighted-average assumptions:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2020	2019	2020	2019
Fair Value Assumptions
Expected volatility	93.0% - 93.5%	80.2% - 80.4%	81.2% - 93.5%	78.4% - 80.4%
Expected dividend yield	0%	0%	0%	0%
Expected term (in years)	5.6 - 5.6	6.0 - 6.1	5.6 - 6.1	5.9 - 6.1
Risk-free interest rate	0.3%	1.6% - 1.8%	0.3% - 1.4%	1.6% - 2.4%

We estimated the fair value of shares under the 2020 ESPP using the Black-Scholes option-pricing model for the three and nine months ended September 30, 2020 and 2019 using the following weighted-average assumptions:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2020	2019	2020	2019
Fair Value Assumptions
Expected volatility	109.7% - 158.2%	N/A	107.0% - 158.2%	N/A
Expected dividend yield	0%	N/A	0%	N/A
Expected term (in years)	0.4 - 1.9	N/A	0.4 - 1.9	N/A
Risk-free interest rate	0.2%	N/A	0.2%	N/A

We recorded total stock-based compensation expense for the three and nine months ended September 30, 2020 and 2019 related to the 2014 Plan, the 2020 Plan and the 2020 ESPP in the condensed statements of operations and allocated the amounts as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
	(In thousands)				(In thousands)
Research and development	$	558	$	88	$	1,081	$	262
General and administrative		1,280		178		2,418		548
Total	$	1,838	$	266	$	3,499	$	810

Upon our IPO, 362,935 performance-based awards vested and, as a result, we recognized $0.3 million of stock-based compensation expense during the three months ended June 30, 2020, which amount is included in the above table for the nine months ended September 30, 2020.

Funding Arrangement

9 Months Ended

Sep. 30, 2020

Funding Arrangement [Abstract]

Funding Arrangement

10. Funding Arrangement

In July 2019, we received a cost-reimbursement research award from Combating Antibiotic Resistant Bacteria Biopharmaceutical Accelerator (“CARB-X”), a public-private partnership funded under a Cooperative Agreement from Assistant Secretary for Preparedness and Response/Biomedical Advanced Research and Development Authority (“BARDA”) and by awards from Wellcome Trust, Germany’s Federal Ministry of Education and Research, the United Kingdom Global Antimicrobial Resistance Innovation Fund and the Bill & Melinda Gates Foundation. In connection with this funding, we entered into a cost-reimbursement sub-award agreement with the Trustees of Boston University, the administrator of the program. The initial award provided the potential for funding up to four years to develop a universal vaccine to prevent infections caused by Group A Strep bacteria, which include pharyngitis, impetigo and necrotizing fasciitis, at an amount equal to 50% of reimbursable expenses up to specified amounts. The initial award committed initial funding of up to $1.6 million and, subject to a CARB-X decision to extend the options, up to $15.1 million in total funding available upon achievement of development milestones over the next four years. Specified research expenditures are reimbursable expenses associated with agreed-upon activities needed to advance the research project supported by the grant. These expenditures can include labor, laboratory supplies, travel, consulting and third-party vendor research and development support costs.

Income from grants is recognized in the period during which the related specified expenses are incurred, provided that the conditions under which the grants were provided have been met. We recognized $0.8 million and $0.1 million of grant income under this award and recorded the amounts in Other income (expense), net in the statement of operations and comprehensive loss during the three months ended September 30, 2020 and 2019, respectively. We recognized $2.2 million and $0.1 million of grant income for the nine months ended September 30, 2020 and 2019, respectively. A grant receivable of $0.8 million and $0.2 million representing unreimbursed, eligible costs incurred under the CARB-X agreement was recorded and included in prepaid expenses and other current assets in the balance sheet as of September 30, 2020 and December 31, 2019, respectively.

In July 2020, the CARB-X agreement was amended to increase the funding percentage for reimbursable expenses during the initial funding period from 50% to 90%. As a result, the initial funding amount increased from $1.6 million to $2.7 million. We anticipate that the increase in the funding percentage for reimbursable expenses may apply to future funding periods and, if so, the total funding amount over the four-year period, if the options to extend are exercised by CARB-X, would increase from the $15.1 million in the original agreement.

Net Loss Per Share

9 Months Ended

Sep. 30, 2020

Earnings Per Share [Abstract]

Net Loss Per Share

11. Net Loss Per Share

The following table sets forth the computation of basic and diluted net loss per share and excludes shares which are legally outstanding, but subject to repurchase by us:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2019			2020			2019
Net loss (in thousands)	$	(21,018	)	$	(11,317	)	$	(68,480	)	$	(35,653	)
Weighted-average shares outstanding used in computing net loss per share, basic and diluted		50,895,358			3,857,298			22,354,212			3,737,779
Net loss per share, basic and diluted	$	(0.41	)	$	(2.93	)	$	(3.06	)	$	(9.54	)

The following potentially dilutive securities were excluded from the computation of diluted net loss per share for the period presented because including them would have been antidilutive:

	Nine Months Ended September 30,
	2020		2019
Stock options		5,094,669		3,071,058
Redeemable convertible preferred stock:
Series A		—		6,225,719
Series B		—		6,786,896
Series C		—		3,688,740
Common stock warrant		—		31,857
Redeemable convertible preferred stock warrant		—		59,276
Total		5,094,669		19,863,546

Income Taxes

9 Months Ended

Sep. 30, 2020

Income Tax Disclosure [Abstract]

Income Taxes

12. Income Taxes

In determining quarterly provisions for income taxes, we use the annual estimated effective tax rate applied to the actual year-to-date profit or loss, adjusted for discrete items arising in that period. Our annual estimated effective tax rate differs from the U.S. federal statutory rate primarily as a result of state taxes and changes in our valuation allowance against our deferred tax assets. For all periods presented, we have incurred net pre-tax losses in the United States. During the three and nine months ended September 30, 2020, there were no material changes to our unrecognized tax benefits, and we do not expect to have any significant changes to unrecognized tax benefits through the end of the fiscal year. For the three and nine months ended September 30, 2020, we reported zero tax provision. We do not have any tax audits or other tax matters pending.

On March 27, 2020, the President of the United States signed into law the Coronavirus Aid, Relief, and Economic Security Act (CARES Act). The CARES Act, among other things, includes certain income tax provisions for individuals and corporations; however, these benefits do not impact our current tax provision.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Related Party Transactions

9 Months Ended

Sep. 30, 2020

Related Party Transactions

13. Related Party Transactions

We have an ongoing relationship with Sutro Biopharma. In 2013, Sutro Biopharma provided support to facilitate the establishment of our Company. As of September 30, 2020 and December 31, 2019, Sutro Biopharma owned approximately 1.6 million shares of our common stock. As of December 31, 2019, Sutro Biopharma also owned warrants to purchase 31,857 shares of our common stock (the “Common Stock Warrant”) at an exercise price of $0.79289 per share and 59,276 shares of our Series C redeemable convertible stock (the “Preferred Stock Warrant”) at an exercise price of $11.5215 per share. The Common Stock Warrant and the Preferred Stock Warrant were automatically net exercised pursuant to their terms for 30,278 shares and 16,591 shares, respectively, of our common stock in connection with the IPO. In the agreements and amendments identified herein, we licensed certain intellectual property and acquired certain supply rights from Sutro Biopharma, including the right to use the XpressCF platform to discover and develop vaccine candidates for the treatment or prophylaxis of infectious diseases. On October 12, 2015, we and Sutro Biopharma (“the Parties”) entered into the Sutro Biopharma License Agreement, which amended and restated an agreement dated August 1, 2014. The Sutro Biopharma License Agreement was subsequently amended on May 9, 2018 (“License Amendment A1”) and May 29, 2018 (“License Amendment A2”). In consideration for the License Amendment A2, we issued to Sutro Biopharma the Preferred Stock Warrant to purchase 59,276 shares of Series C redeemable convertible preferred stock at a purchase price of $11.5215 per share. We also entered into a separate supply agreement with Sutro Biopharma on May 29, 2018 (the “Sutro Biopharma Supply Agreement”).

Under the Sutro Biopharma License Agreement, Sutro Biopharma granted us an exclusive, worldwide license to research, develop, manufacture and commercialize vaccine products addressing infectious disease, which are discovered or produced based on the use of Sutro Biopharma’s proprietary cell-free protein expression technology, known as XpressCF, which utilizes extracts derived from strains of E. coli. In connection with the Sutro Biopharma License Agreement, under the Sutro Biopharma Supply Agreement, Sutro Biopharma has agreed to manufacture and supply extracts and reagents for us on a cost-plus basis. In consideration for the rights licensed, we are obligated to pay a 4% royalty on worldwide aggregate annual net sales of our vaccine products for human health and a 2% royalty on such net sales of vaccine products for animal health. In addition, for a certain period of time, if we grant a sublicense to a third party to further develop or sell a vaccine product discovered or generated by us, we are obligated to pay Sutro Biopharma a percentage, in the low single digits, of any net sublicense fees received. Our obligation to pay single-digit royalties to Sutro Biopharma expires on a country-by-country basis on the later of the expiration of the last to expire patent covering the manufacture, use, offer for sale or importation of the applicable vaccine product and ten years from first commercial sale of the applicable vaccine product. Our obligation to pay sublicense fees to Sutro Biopharma expired in July 2020. In License Amendment A1, the Parties amended the license agreement to remove a pre-IND regulatory meeting as a diligence milestone and to agree that certain other diligence milestones had been satisfied. In License Amendment A2, the Parties amended the license agreement to add certain terms confirming our obligation to purchase Sutro Biopharma’s proprietary extract from E. coli (“Extract”) from Sutro Biopharma. In addition, the Parties amended the license agreement to specify our rights to a transfer of certain know-how relating to the manufacture of Extract in the event of a declaration of bankruptcy by Sutro Biopharma. Finally, the Parties agreed to terms providing for injunctive relief in the event of a breach or threatened breach by the other party.

In the Sutro Biopharma Supply Agreement, the Parties agreed to terms for the supply of manufactured Extract and custom reagents by Sutro Biopharma for us to use in manufacturing vaccine compositions in non-clinical research or in Phase 1 or Phase 2 clinical trials. The term of the Sutro Biopharma Supply Agreement is from execution until the later of July 31, 2021 and the date the parties enter into and commence activities under the supply agreement unless extended through a subsequent supply agreement for the supply of Extract and custom reagents for vaccine compositions for Phase 3 and commercial uses as contemplated in the Supply Agreement.

We recognized expense related to the Supply Agreement of $0.1 million and $1.0 million for the three months ended September 30, 2020 and 2019, respectively. We recognized expense of $0.3 million and $1.1 million for the nine months ended September 30, 2020 and 2019, respectively. In addition, we recorded $0 and less than $0.1 million in changes in the fair value of the Preferred Stock Warrant for the three months ended September 30, 2020 and 2019, respectively, and $0.2 million and less than $0.1 million for the nine months ended September 30, 2020 and 2019, respectively. The expense related to the changes in the fair value of the warrant is included in research and development expenses in the condensed statements of operations and comprehensive loss. Accrued expenses payable to Sutro Biopharma were $0.1 million and less than $0.1 million as of September 30, 2020 and December 31, 2019, respectively.

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These condensed financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and footnote disclosures normally included in the financial statements prepared in accordance with U.S. GAAP have been condensed or omitted in accordance with such rules and regulations. Certain changes in presentation were made in the condensed balance sheet as of December 31, 2019 to conform to the presentation of the condensed balance sheet as of September 30, 2020.
Unaudited Interim Condensed Financial Statements	Unaudited Interim Condensed Financial Statements The condensed balance sheet as of September 30, 2020, the condensed statements of operations and comprehensive loss, redeemable convertible preferred stock and stockholders’ equity (deficit) for the three and nine months ended September 30, 2020 and 2019, and the condensed statements of cash flows for the nine months ended September 30, 2020 and 2019, are unaudited. The unaudited interim condensed financial statements have been prepared on the same basis as the audited annual financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair statement of our financial information. The financial data disclosed in the footnotes to the condensed financial statements related to the three and nine months ended September 30, 2020 and 2019 are also unaudited. The results of operations for the three and nine months ended September 30, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any other future annual or interim period. These interim condensed financial statements should be read in conjunction with our audited annual financial statements included in the prospectus dated June 11, 2020 that forms a part of our Registration Statements on Form S-1 (File Nos. 333-238630 and 333-239110) as filed with the SEC pursuant to Rule 424(b)(4) and Rule 462(b) promulgated under the Securities Act of 1933, as amended.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities at the date of the financial statements. On an ongoing basis, we evaluate our estimates and assumptions, including those related to stock-based compensation expense, accruals for certain research and development costs, the valuation of deferred tax assets and income taxes. Management bases our estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. Actual results may differ materially from those estimates.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average of shares of common stock outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is the same as basic net loss per share, since the effects of potentially dilutive securities are antidilutive given the net loss for each period presented.
Deferred Offering Costs	Deferred Offering Costs Deferred offering costs consist of fees and expenses incurred in connection with the sale of our common stock in the IPO, including legal, accounting, printing and other IPO-related costs. Prior to the completion of our IPO, deferred offering costs were included in Other assets on the condensed balance sheet. In connection with and as of the closing of our IPO, these costs were reclassified to Additional paid-in capital, representing a reduction to the IPO proceeds. As of September 30, 2020, $3.4 million of these IPO-related costs are included in the Additional paid-in capital line item on the condensed balance sheet. As of December 31, 2019, $1.1 million of deferred offering costs were included in Other assets on the balance sheet.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject us to a concentration of credit risk consist primarily of cash and cash equivalents. We currently invest in money market funds. We maintain bank deposits in federally insured financial institutions and these deposits may exceed federally insured limits. We are exposed to credit risk in the event of a default by the financial institutions holding our cash and cash equivalents. We have not experienced any losses on our deposits of cash and cash equivalents. We are subject to supplier concentration risk from our suppliers. We source our critical raw materials from a sole source supplier, Sutro Biopharma, Inc. (“Sutro Biopharma”). We also use one contract manufacturing organization (“CMO”), Lonza Ltd. (“Lonza”), to handle most of our manufacturing activities. If we were to experience disruptions in raw materials supplied by Sutro Biopharma, or in manufacturing activities at Lonza, we may experience significant delays in our product development timelines and may incur substantial costs to secure alternative sources of raw materials or manufacturing. Our future results of operations involve a number of other risks and uncertainties. Factors that could affect our future operating results and cause actual results to vary materially from expectations include, but are not limited to, our early stages of clinical vaccine development; our ability to advance vaccine candidates into, and successfully complete, clinical trials on the timelines we project; our ability to adequately demonstrate sufficient safety and efficacy of our vaccine candidates; our ability to enroll subjects in our ongoing and future clinical trials; our ability to successfully manufacture and supply our vaccine candidates for clinical trials; our ability to obtain additional capital to finance our operations; our ability to obtain, maintain and protect our intellectual property rights; developments relating to our competitors and our industry, including competing vaccine candidates; general and market conditions; and other risks and uncertainties, including those more fully described in the “Risk Factors” section of this Quarterly Report on Form 10-Q.
Recently Issued Accounting Pronouncements Adopted And Not Yet Adopted	Recently Adopted Accounting Pronouncements In June 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2018-07, Improvements to Nonemployee Share-Based Payment Accounting, which simplifies the accounting for share-based payments granted to non-employees for goods and services. This standard expands the scope of Topic 718, Compensation-Stock Compensation, to include share-based payments issued to non-employees for goods and services. Consequently, the accounting for share-based payments to non-employees and employees was substantially aligned. The ASU supersedes Subtopic 505-50, Equity—Equity-Based Payments to Non-Employees. This standard is effective for fiscal years beginning after December 15, 2019 and interim periods within fiscal years beginning after December 15, 2020. The standard should be adopted on a modified retrospective basis which recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. We adopted this ASU as of January 1, 2020. The adoption of this ASU had no material impact on our financial statements or disclosures. Recently Issued Accounting Pronouncements—Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). ASU 2016-02 was subsequently amended by ASU 2018-01, ASU 2018-10, ASU 2018-11, ASU 2018-20, ASU 2019-01, ASU 2019-10 and ASU 2020-05, which the FASB issued in January 2018, July 2018, July 2018, December 2018, March 2019, November 2019 and June 2020, respectively (collectively, the “amended ASU 2016-02”). The amended ASU 2016-02 requires lessees to recognize leases on the balance sheet and disclose key information about leasing arrangements. The new standard establishes a right-of-use (“ROU”) model that requires a lessee to recognize a ROU asset and a lease liability on the balance sheet for all leases with a term longer than 12 months. Under the new standard, leases will be classified as either finance leases or operating leases, with classification affecting the pattern and classification of expense recognition in the income statement. The new standard is effective for us on January 1, 2022, with early adoption permitted. We expect to adopt the new standard on the effective date. The new standard requires an entity to adopt using one of two approaches, either (i) retrospectively to each prior reporting period presented in the financial statements with the cumulative effect recognized at the beginning of the earliest comparative period presented, or (ii) retrospectively at the beginning of the period of adoption through a cumulative-effect adjustment. Although we are currently evaluating the impact of adoption on our financial statements and related disclosures, we believe the most significant changes will be the recognition of the ROU assets and the related lease liabilities for our operating leases on our condensed balance sheets. In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740). The amendments in ASU 2019-12 simplify the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The amendments also improve consistent application of and simplify U.S. GAAP or other areas of Topic 740 by clarifying and amending existing guidance. The new standard is effective for us on January 1, 2022 and for interim periods beginning on January 1, 2023. We are currently evaluating the impact that the standard will have on our condensed financial statements and related disclosures.

Fair Value Measurements and Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2020

Fair Value Disclosures [Abstract]

Schedule of Inputs Used for Level 3 Liability

Below are inputs used for the Level 3 liability as of December 31, 2019:

	December 31, 2019
	Redeemable Convertible Preferred Stock Warrant
Value of Series C Redeemable Preferred Stock Per Share	$	6.82
Risk-Free Rate		1.90	%
Volatility		73.5	%
Term in Years	8.42

Schedule of Financial Instruments Measured at Fair Value on Recurring Basis

The following tables set forth our financial instruments measured at fair value on a recurring basis by level within the fair value hierarchy at September 30, 2020 and December 31, 2019:

	September 30, 2020
	Total		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds ⁽¹⁾	$	392,272	$	392,272	$	—	$	—

	December 31, 2019
	Total Fair Value		Level 1		Level 2		Level 3
	(In thousands)
Assets:
Money market funds ⁽¹⁾	$	48,168	$	48,168	$	—	$	—
Liabilities:
Redeemable convertible preferred stock warrant liability	$	450	$	—	$	—	$	450

(1)	Included within cash and cash equivalents on the condensed balance sheet.

Summary of Changes in Estimated Fair Value of Level 3 Financial Instruments

	Warrant Liability
	(in thousands)
Balance — December 31, 2019	$	450
Change in fair value		179
Balance — March 31, 2020		629
Warrant liability write-off upon IPO		(629	)
Balance — June 30, 2020	$	—

Balance Sheet Details (Tables)

9 Months Ended

Sep. 30, 2020

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net as of September 30, 2020 and December 31, 2019 consisted of the following:

	September 30,			December 31,
	2020			2019
	(in thousands)
Furniture and equipment	$	397		$	397
Computers and computer software		169			146
Lab equipment		3,887			3,260
Leasehold improvements		1,903			1,884
Capital leases — lab equipment		—			686
Construction in Progress		14			—
Total property and equipment		6,370			6,373
Less: accumulated depreciation and amortization		(3,831	)		(2,982	)
Property and equipment, net	$	2,539		$	3,391

Property and equipment, net at December 31, 2019 included the following amounts for leases that have been capitalized:

	Useful Life (Years)	December 31, 2019
		(in thousands)
Capital lease equipment	3 - 5	$	686
Less: accumulated amortization			(471	)
		$	215

Schedule of Accrued Expenses

Accrued expenses as of September 30, 2020 and December 31, 2019 consisted of the following:

	September 30,		December 31,
	2020		2019
	(in thousands)
Preclinical studies	$	1,969	$	844
Professional fees		486		397
Other accrued expenses		415		64
Total	$	2,870	$	1,305

Commitments and Contingencies (Tables)

9 Months Ended

Sep. 30, 2020

Commitments And Contingencies Disclosure [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net as of September 30, 2020 and December 31, 2019 consisted of the following:

	September 30,			December 31,
	2020			2019
	(in thousands)
Furniture and equipment	$	397		$	397
Computers and computer software		169			146
Lab equipment		3,887			3,260
Leasehold improvements		1,903			1,884
Capital leases — lab equipment		—			686
Construction in Progress		14			—
Total property and equipment		6,370			6,373
Less: accumulated depreciation and amortization		(3,831	)		(2,982	)
Property and equipment, net	$	2,539		$	3,391

Property and equipment, net at December 31, 2019 included the following amounts for leases that have been capitalized:

	Useful Life (Years)	December 31, 2019
		(in thousands)
Capital lease equipment	3 - 5	$	686
Less: accumulated amortization			(471	)
		$	215

Schedule of Future Minimum Payments under Operating Leases

Future minimum payments required under operating leases as of September 30, 2020 are as follows:

	(in thousands)
Remainder of 2020	$	183
2021		531
Total future minimum payments	$	714

Redeemable Convertible Preferred Stock (Tables)

9 Months Ended

Sep. 30, 2020

Temporary Equity Disclosure [Abstract]

Summary of Convertible Preferred Stock

The authorized, issued and outstanding shares of redeemable convertible preferred stock and liquidation preferences as of December 31, 2019 were as follows:

	December 31, 2019
	Shares Authorized		Issued and Outstanding		Original Issuance Price		Carrying Value		Liquidation Preference
							(In thousands)
Series A Redeemable Convertible Preferred		10,502,804		6,225,719	$	4.32	$	24,967	$	26,887
Series B Redeemable Convertible Preferred		11,449,515		6,786,896		8.86		55,151		60,150
Series C Redeemable Convertible Preferred		14,010,043		7,377,480		11.52		80,192		85,000
		35,962,362		20,390,095			$	160,310	$	172,037

Common Stock (Tables)

9 Months Ended

Sep. 30, 2020

Equity [Abstract]

Schedule of Common Stock Shares Reserved for Future Issuance

	September 30,		December 31,
	2020		2019
Options issued and outstanding		5,094,669		3,364,568
Shares available for future stock option grants		4,839,649		835,941
Conversion of redeemable convertible preferred stock		—		20,390,095
Common stock warrant		—		31,857
Redeemable convertible preferred stock warrant		—		59,276
Total		9,934,318		24,681,737

Warrants (Tables)

9 Months Ended

Sep. 30, 2020

Equity [Abstract]

Summary of Warrants Issued and Outstanding

Warrants issued and outstanding as of December 31, 2019 were as follows:

Warrants to Purchase Stock

Number of

Warrants

Issued and

Outstanding

Issue Date

Expiration

Date

Exercise

Price

Common stock

31,857

July 10, 2015

July 10, 2025

0.79

Series C redeemable convertible preferred stock

59,276

May 29, 2018

May 29, 2028

11.52

Total

91,133

Equity Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2020

Summary of Estimated Fair Value of Employee Stock Options

	Three Months Ended September 30,		Nine Months Ended September 30,
	2020	2019	2020	2019
Fair Value Assumptions
Expected volatility	93.0% - 93.5%	80.2% - 80.4%	81.2% - 93.5%	78.4% - 80.4%
Expected dividend yield	0%	0%	0%	0%
Expected term (in years)	5.6 - 5.6	6.0 - 6.1	5.6 - 6.1	5.9 - 6.1
Risk-free interest rate	0.3%	1.6% - 1.8%	0.3% - 1.4%	1.6% - 2.4%

2020 Plan and 2014 Plan

Summary of Activity Under Stock Option Plans

Activity under our 2020 Plan and 2014 Plan, which excludes options to purchase 66,982 shares granted outside of the 2020 Plan and 2014 Plan, was as follows:

				Options Outstanding
Stock Option Activity	Options Available for Grant			Number of Options			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balances — December 31, 2019		835,941			3,297,586		$	1.93
Additional shares authorized		5,997,435			—
Options granted		(2,065,590	)		2,065,590		$	6.57
Options exercised		—			(263,626	)	$	1.86
Options forfeited		71,863			(71,863	)	$	2.47
Balances — September 30, 2020		4,839,649			5,027,687		$	3.83		8.22	$	228,992
Vested and expected to vest — September 30, 2020					5,027,687		$	3.83		8.22	$	228,992
Exercisable at September 30, 2020					1,782,595		$	1.85		6.70	$	84,725

2020 Employee Stock Purchase Plan

Summary of Estimated Fair Value of Shares Under Employee Stock Purchase Plan

	Three Months Ended September 30,		Nine Months Ended September 30,
	2020	2019	2020	2019
Fair Value Assumptions
Expected volatility	109.7% - 158.2%	N/A	107.0% - 158.2%	N/A
Expected dividend yield	0%	N/A	0%	N/A
Expected term (in years)	0.4 - 1.9	N/A	0.4 - 1.9	N/A
Risk-free interest rate	0.2%	N/A	0.2%	N/A

2014 Plan, 2020 Plan and 2020 ESPP

Summary of Stock-based Compensation Expense

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
	(In thousands)				(In thousands)
Research and development	$	558	$	88	$	1,081	$	262
General and administrative		1,280		178		2,418		548
Total	$	1,838	$	266	$	3,499	$	810

Net Loss Per Share (Tables)

9 Months Ended

Sep. 30, 2020

Earnings Per Share [Abstract]

Schedule of Computation of Basic and Diluted Net Loss Per Share

The following table sets forth the computation of basic and diluted net loss per share and excludes shares which are legally outstanding, but subject to repurchase by us:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2019			2020			2019
Net loss (in thousands)	$	(21,018	)	$	(11,317	)	$	(68,480	)	$	(35,653	)
Weighted-average shares outstanding used in computing net loss per share, basic and diluted		50,895,358			3,857,298			22,354,212			3,737,779
Net loss per share, basic and diluted	$	(0.41	)	$	(2.93	)	$	(3.06	)	$	(9.54	)

Schedule of Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss Per Share

The following potentially dilutive securities were excluded from the computation of diluted net loss per share for the period presented because including them would have been antidilutive:

	Nine Months Ended September 30,
	2020		2019
Stock options		5,094,669		3,071,058
Redeemable convertible preferred stock:
Series A		—		6,225,719
Series B		—		6,786,896
Series C		—		3,688,740
Common stock warrant		—		31,857
Redeemable convertible preferred stock warrant		—		59,276
Total		5,094,669		19,863,546

Company Organization and Nature of Business - Additional Information (Details) $ / shares in Units, $ in Thousands			1 Months Ended	3 Months Ended	9 Months Ended
	Jun. 15, 2020 shares	Jun. 05, 2020	Jun. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2020 $ / shares shares	Sep. 30, 2020 USD ($) shares	Jun. 17, 2020 shares	Dec. 31, 2019 shares
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Reverse stock split		one-for-1.6870
Reverse stock split, conversion ratio		0.593
Net proceeds from initial public offering \| $			$ 264,000
Underwriting discounts and commissions \| $			20,100
Offering expenses \| $			$ 3,400		$ 3,368
Redeemable convertible preferred stock, shares outstanding							20,390,095
Redeemable Convertible Preferred Stock
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Conversion of preferred stock (in shares)			28,610,337
Redeemable convertible preferred stock, shares outstanding					0	0
Common Stock
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Shares issued and sold				17,968,750
Conversion of preferred stock (in shares)	28,610,337			28,610,337
Initial Public Offering
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Shares issued and sold			17,968,750
Underwriters’ option to purchase additional shares			2,343,750
Public offering price per share \| $ / shares			$ 16.00	$ 16.00
Pneumococcal Conjugate Vaccine
Schedule Of Organization Consolidation And Presentation Of Financial Statements [Line Items]
Global target revenue \| $					$ 7,000,000

Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
ASU 2018-07
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Accounting standard update adopted	true
Accounting standard update material impact	true
Accounting standard update adoption date	Jan. 01, 2020
Additional Paid-in Capital
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
IPO-related costs	$ 3.4
Other Assets
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Deferred offering costs		$ 1.1

- Definition

Indicates (true false) whether accounting standards update was adopted.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-SubTopic 10
-Section 65
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 65
-Paragraph 15
-Subparagraph (a)
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 1
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 815
-SubTopic 20
-Section 65
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121483254&loc=SL120254523-199619

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 65
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=120154821&loc=SL120154904-197079

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 926
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-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120154821&loc=SL120154904-197079

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

- Definition

Date accounting standards update was adopted, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants outstanding			91,133
Fair value assets transferred from level 1 to level 2	$ 0	$ 0	$ 0
Fair value assets transferred from level 2 to level 1	0	0	0
Fair value liabilities transferred from level 1 to level 2	0	0	0
Fair value liabilities transferred from level 2 to level 1	0	0	0
Fair value assets transferred into level 3	0	0	0
Fair value assets transferred out of level 3	0	0	0
Fair value liabilities transferred into level 3	0	0	0
Fair value liabilities transferred out of level 3	0	$ 0	$ 0
Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
New warrant liabilities issued	$ 0
Redeemable Convertible Preferred Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants outstanding	0	0

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Inputs Used for Level 3 Liability (Details) - Level 3 - Fair Value, Recurring - Option Pricing Model - Redeemable Convertible Preferred Stock Warrant	Dec. 31, 2019
Value of Series C Redeemable Preferred Stock Per Share
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and rights outstanding measurement input	6.82
Risk Free Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and rights outstanding measurement input	1.90%
Volatility
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and rights outstanding measurement input	73.50%
Term in Years
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and rights outstanding measurement input	8 years 5 months 1 day

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Financial Instruments Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring - USD ($)
$ in Thousands

Sep. 30, 2020

Dec. 31, 2019

Redeemable Convertible Preferred Stock Warrant Liability

Liabilities:

Liabilities, Fair Value Disclosure

$ 450

Level 3 | Redeemable Convertible Preferred Stock Warrant Liability

Liabilities:

Liabilities, Fair Value Disclosure

450

Money Market Funds

Assets:

Assets, Fair Value Disclosure

^[1]

$ 392,272

48,168

Money Market Funds | Level 1

Assets:

Assets, Fair Value Disclosure

^[1]

$ 392,272

$ 48,168

[1]	Included within cash and cash equivalents on the condensed balance sheet.

Fair Value Measurements and Fair Value of Financial Instruments - Summary of Changes in Estimated Fair Value of Level 3 Financial Instruments (Details) - Warrant Liability - Level 3 - USD ($) $ in Thousands	3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance	$ 629	$ 450
Change in fair value		179
Warrant liability write-off upon IPO	$ (629)
Balance		$ 629

Balance Sheet Details - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Total property and equipment	$ 6,370	$ 6,373
Less: accumulated depreciation and amortization	(3,831)	(2,982)
Property and equipment, net	2,539	3,391
Furniture and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	397	397
Computers and Computer Software
Property Plant And Equipment [Line Items]
Total property and equipment	169	146
Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	3,887	3,260
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	1,903	1,884
Capital Leases — Lab Equipment
Property Plant And Equipment [Line Items]
Total property and equipment		686
Less: accumulated depreciation and amortization		(471)
Property and equipment, net		$ 215
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 14

Balance Sheet Details - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Property Plant And Equipment [Line Items]
Depreciation and amortization expense	$ 300	$ 300	$ 1,100	$ 900
Capital lease amortization expense	$ 0	$ 100		$ 200
Maximum
Property Plant And Equipment [Line Items]
Capital lease amortization expense			$ 100

Balance Sheet Details - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accrued Liabilities Current [Abstract]
Preclinical studies	$ 1,969	$ 844
Professional fees	486	397
Other accrued expenses	415	64
Total	$ 2,870	$ 1,305

Commitments and Contingencies - Additional Information (Details)		1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 30, 2018 USD ($)	Mar. 31, 2020 piece	Oct. 31, 2019 piece	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Lease term				36 months		36 months
Present value of annual rental payments including guaranteed residual value, percentage						90.00%
Lease buyout agreement, number of lab equipment \| piece		2	2
Lease buyout agreement, remaining balance of lease liability				$ 0		$ 0
Future minimum payments required under capital leases				$ 0		$ 0
Operating lease, agreement term				5 years		5 years
Operating lease, renewal term				30 months		30 months
Operating lease, description						In July 2016, we entered into a five-year lease agreement for our headquarters facility located in Foster City, California. The term of the lease is from September 1, 2016 to August 31, 2021, with two 30-month renewal options.
Operating leases, rent expense recognized				$ 200,000	$ 200,000	$ 500,000	$ 400,000
Lonza DMSA
Loss Contingencies [Line Items]
Amount recorded with respect to the potential future payments above the initial cash cap				$ 0		$ 0		$ 0
Minimum
Loss Contingencies [Line Items]
Lease interest rate				6.90%		6.90%
Maximum
Loss Contingencies [Line Items]
Lease interest rate				15.00%		15.00%
Maximum \| Lonza DMSA
Loss Contingencies [Line Items]
Payments in equity, percentage	25.00%
Payments in equity, amount	$ 2,500,000
Equity payment, upper limit	$ 10,000,000

Commitments and Contingencies - Schedule of Property and Equipment Amounts for Capital Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 6,373	$ 6,370
Less: accumulated depreciation and amortization	(2,982)	(3,831)
Property and equipment, net	3,391	$ 2,539
Capital Lease Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	686
Less: accumulated depreciation and amortization	(471)
Property and equipment, net	$ 215
Capital Lease Equipment \| Minimum
Property Plant And Equipment [Line Items]
Useful life	3 years
Capital Lease Equipment \| Maximum
Property Plant And Equipment [Line Items]
Useful life	5 years

Commitments and Contingencies - Schedule of Future Minimum Payments under Operating Leases (Details) $ in Thousands	Sep. 30, 2020 USD ($)
Commitments And Contingencies Disclosure [Abstract]
Remainder of 2020	$ 183
2021	531
Total future minimum payments	$ 714

Redeemable Convertible Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Jun. 17, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares outstanding							20,390,095
Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock converted into common stock	28,610,337
Redeemable convertible preferred stock, shares outstanding					0	0
Series D Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock, shares issued		8,220,242		8,220,242
Purchase price per share		$ 13.3816		$ 13.3816
Aggregate purchase price		$ 110,000	$ 4	$ 109,875
Redeemable convertible preferred stock, shares outstanding		8,220,242		8,220,242

Redeemable Convertible Preferred Stock - Summary of Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized			35,962,362
Redeemable convertible preferred stock, shares issued			20,390,095
Redeemable convertible preferred stock, shares outstanding			20,390,095
Redeemable convertible preferred stock value			$ 160,310
Redeemable convertible preferred stock, liquidation value			$ 172,037
Series A Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized	10,502,804		10,502,804
Redeemable convertible preferred stock, shares issued	0		6,225,719
Redeemable convertible preferred stock, shares outstanding	0	6,225,719	6,225,719	6,225,719	6,225,719	6,225,719	6,225,719
Public offering price per share			$ 4.32
Redeemable convertible preferred stock value		$ 24,967	$ 24,967	$ 24,967	$ 24,967	$ 24,967	$ 24,967
Redeemable convertible preferred stock, liquidation value	$ 0		$ 26,887
Series B Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized	11,449,515		11,449,515
Redeemable convertible preferred stock, shares issued	0		6,786,896
Redeemable convertible preferred stock, shares outstanding	0	6,786,896	6,786,896	6,786,896	6,786,896	6,786,896	6,786,896
Public offering price per share			$ 8.86
Redeemable convertible preferred stock value		$ 55,151	$ 55,151	$ 55,151	$ 55,151	$ 55,151	$ 55,151
Redeemable convertible preferred stock, liquidation value	$ 0		$ 60,150
Series C Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Redeemable convertible preferred stock, shares authorized	12,545,824		14,010,043
Redeemable convertible preferred stock, shares issued	0		7,377,480
Redeemable convertible preferred stock, shares outstanding	0	7,377,480	7,377,480	3,688,740	3,688,740	3,688,740	3,688,740
Public offering price per share			$ 11.52
Redeemable convertible preferred stock value		$ 80,192	$ 80,192	$ 37,692	$ 37,692	$ 37,692	$ 37,692
Redeemable convertible preferred stock, liquidation value	$ 0		$ 85,000

Common Stock - Additional Information (Details) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Equity [Abstract]
Common stock, shares authorized	500,000,000	52,000,000
Common stock, par value per share	$ 0.001	$ 0.001
Common stock, shares issued	50,949,490	4,059,909
Common stock, shares outstanding	50,949,490	4,059,909
Common stock, dividends, per share, declared	$ 0	$ 0
Common stock, voting rights	Each share of common stock is entitled to one vote.
Equity incentive plan, shares issued	66,982

Common Stock - Schedule of Common Stock Shares Reserved for Future Issuance (Details) - 2020 Plan and 2014 Plan - shares	Sep. 30, 2020	Dec. 31, 2019
Class Of Stock [Line Items]
Reserved common stock for future issuances	9,934,318	24,681,737
Options Issued and Outstanding
Class Of Stock [Line Items]
Reserved common stock for future issuances	5,094,669	3,364,568
Shares Available for Future Stock Option Grants
Class Of Stock [Line Items]
Reserved common stock for future issuances	4,839,649	835,941
Conversion of Redeemable Convertible Preferred Stock
Class Of Stock [Line Items]
Reserved common stock for future issuances		20,390,095
Redeemable Convertible Preferred Stock Warrant
Class Of Stock [Line Items]
Reserved common stock for future issuances		59,276
Common Stock Warrant
Class Of Stock [Line Items]
Reserved common stock for future issuances		31,857

Warrants - Additional Information (Details)	Jun. 30, 2020 shares
Common Stock Warrant \| Series C Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Warrant exercised	46,869

Warrants - Summary of Warrants Issued and Outstanding (Details)	12 Months Ended
	Dec. 31, 2019 $ / shares shares
Class Of Warrant Or Right [Line Items]
Number of Warrants Issued and Outstanding	91,133
Series C Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Number of Warrants Issued and Outstanding	59,276
Issue Date	May 29, 2018
Expiration Date	May 29, 2028
Exercise Price \| $ / shares	$ 11.52
Common Stock
Class Of Warrant Or Right [Line Items]
Number of Warrants Issued and Outstanding	31,857
Issue Date	Jul. 10, 2015
Expiration Date	Jul. 10, 2025
Exercise Price \| $ / shares	$ 0.79

Equity Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended			9 Months Ended
	Jun. 11, 2020	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Early exercised stock options		22,700			22,700		86,409
Options granted					66,982
Exercise of stock options (in shares)		67,792		279,947	263,626	280,836
Weighted-average price per share		$ 1.60		$ 1.55	$ 1.86	$ 1.55
Weighted-average grant date fair value of options granted		$ 29.83		$ 2.31	$ 8.17	$ 1.51
Intrinsic value of the stock options exercised		$ 2.5		$ 0.2	$ 5.1	$ 0.2
Performance-based Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense			$ 0.3
Performance-based Awards \| IPO
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares vested			362,935
Other Liabilities
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining liabilities related to early exercised shares							$ 0.2
Other Liabilities \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining liabilities related to early exercised shares		$ 0.1			$ 0.1
2020 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance	10,150,000
Term of plan	10 years
Percentage of outstanding number of shares	5.00%
Aggregate number of shares available for issuance		4,839,649			4,839,649
Number of shares outstanding		218,500			218,500
2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding		4,809,187			4,809,187
2020 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance	650,000
Term of plan	10 years
Percentage of outstanding number of shares	1.00%
Aggregate number of shares available for issuance		650,000			650,000
Percentage of payroll deductions of eligible compensation	15.00%

Equity Incentive Plans - Summary of Activity Under Stock Option Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, granted			66,982
Number of Options, exercised	(67,792)	(279,947)	(263,626)	(280,836)
Weighted-Average Exercise Price Per Share, Options exercised	$ 1.60	$ 1.55	$ 1.86	$ 1.55
2020 Plan and 2014 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Available for Grant, Beginning Balance			835,941
Options Available for Grant, Additional shares authorized			5,997,435
Options Available for Grant, granted			(2,065,590)
Options Available for Grant, forfeited			71,863
Options Available for Grant, Ending Balance	4,839,649		4,839,649
Number of Options, Beginning Balance			3,297,586
Number of Options, granted			2,065,590
Number of Options, exercised			(263,626)
Number of Options, forfeited			(71,863)
Number of Options, Ending Balance	5,027,687		5,027,687
Number of Options, Vested and expected to vest	5,027,687		5,027,687
Number of Options, Exercisable	1,782,595		1,782,595
Weighted-Average Exercise Price Per Share, Beginning Balance			$ 1.93
Weighted-Average Exercise Price Per Share, Options granted			6.57
Weighted-Average Exercise Price Per Share, Options exercised			1.86
Weighted-Average Exercise Price Per Share, Options forfeited			2.47
Weighted-Average Exercise Price Per Share, Ending Balance	$ 3.83		3.83
Weighted-Average Exercise Price Per Share, Vested and expected to vest	3.83		3.83
Weighted-Average Exercise Price Per Share, Exercisable	$ 1.85		$ 1.85
Weighted-Average Remaining Contractual Term (Years)			8 years 2 months 19 days
Weighted-Average Remaining Contractual Term (Years), Vested and expected to vest			8 years 2 months 19 days
Weighted-Average Remaining Contractual Term (Years), Exercisable			6 years 8 months 12 days
Aggregate Intrinsic Value	$ 228,992		$ 228,992
Aggregate Intrinsic Value, Vested and expected to vest	228,992		228,992
Aggregate Intrinsic Value, Exercisable	$ 84,725		$ 84,725

Equity Incentive Plans - Summary of Estimated Fair Value of Employee Stock Options (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value Assumptions
Expected volatility, Minimum	93.00%	80.20%	81.20%	78.40%
Expected volatility, Maximum	93.50%	80.40%	93.50%	80.40%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Risk-free interest rate	0.30%
Risk-free interest rate, Minimum		1.60%	0.30%	1.60%
Risk-free interest rate, Maximum		1.80%	1.40%	2.40%
Minimum
Fair Value Assumptions
Expected term (in years)	5 years 7 months 6 days	6 years	5 years 7 months 6 days	5 years 10 months 24 days
Maximum
Fair Value Assumptions
Expected term (in years)	5 years 7 months 6 days	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days

Equity Incentive Plans - Summary of Estimated Fair Value of Shares Under Employee Stock Purchase Plan (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value Assumptions
Expected volatility, Minimum	93.00%	80.20%	81.20%	78.40%
Expected volatility, Maximum	93.50%	80.40%	93.50%	80.40%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Risk-free interest rate	0.30%
Minimum
Fair Value Assumptions
Expected term (in years)	5 years 7 months 6 days	6 years	5 years 7 months 6 days	5 years 10 months 24 days
Maximum
Fair Value Assumptions
Expected term (in years)	5 years 7 months 6 days	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days
2020 Employee Stock Purchase Plan
Fair Value Assumptions
Expected volatility, Minimum	109.70%		107.00%
Expected volatility, Maximum	158.20%		158.20%
Expected dividend yield	0.00%		0.00%
Risk-free interest rate	0.20%		0.20%
2020 Employee Stock Purchase Plan \| Minimum
Fair Value Assumptions
Expected term (in years)	4 months 24 days		4 months 24 days
2020 Employee Stock Purchase Plan \| Maximum
Fair Value Assumptions
Expected term (in years)	1 year 10 months 24 days		1 year 10 months 24 days

Equity Incentive Plans - Summary of Stock-based Compensation Expense (Details) - 2014 Plan, 2020 Plan and 2020 ESPP - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,838	$ 266	$ 3,499	$ 810
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	558	88	1,081	262
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,280	$ 178	$ 2,418	$ 548

Funding Arrangement - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Funding Arrangement [Line Items]
Grant income			$ 787,000	$ 54,000	$ 2,152,000	$ 54,000
Cost Reimbursement Sub-Award Agreement
Funding Arrangement [Line Items]
Funding period of award to develop universal vaccine to prevent infections caused by Group A Strep bacteria		4 years
Percentage of reimbursable expenses		50.00%
Grant income			800,000	$ 100,000	2,200,000	$ 100,000
Cost Reimbursement Sub-Award Agreement \| Maximum
Funding Arrangement [Line Items]
Initial funding committed by award		$ 1,600,000
Total funding committed by award, available upon achievement of development milestones		$ 15,100,000
CARB-X Agreement
Funding Arrangement [Line Items]
Funding period of award to develop universal vaccine to prevent infections caused by Group A Strep bacteria	4 years
Grant receivable on unreimbursed, eligible costs incurred			$ 800,000		$ 800,000		$ 200,000
CARB-X Agreement \| Maximum
Funding Arrangement [Line Items]
Percentage of reimbursable expenses	90.00%
Initial funding committed by award	$ 2,700,000
Total funding committed by award, available upon achievement of development milestones	$ 15,100,000
CARB-X Agreement \| Minimum
Funding Arrangement [Line Items]
Percentage of reimbursable expenses	50.00%
Initial funding committed by award	$ 1,600,000

Net Loss Per Share - Schedule of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net loss (in thousands)	$ (21,018)	$ (11,317)	$ (68,480)	$ (35,653)
Weighted-average shares outstanding used in computing net loss per share, basic and diluted	50,895,358	3,857,298	22,354,212	3,737,779
Net loss per share, basic and diluted	$ (0.41)	$ (2.93)	$ (3.06)	$ (9.54)

- Definition

Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Net Loss Per Share - Schedule of Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - shares	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	5,094,669	19,863,546
Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share	5,094,669	3,071,058
Common Stock Warrant
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share		31,857
Redeemable Convertible Preferred Stock Warrant
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share		59,276
Series A Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share		6,225,719
Series B Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share		6,786,896
Series C Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of diluted net loss per share		3,688,740

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Tax provision	$ 0	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Related Party Transactions - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
	May 29, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jun. 30, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Common stock, shares owned		50,949,490		50,949,490			4,059,909
Change in fair value of redeemable convertible preferred stock warrant				$ 179	$ (12)
Accrued expenses payable		$ 2,870		$ 2,870			$ 1,305
Series C Redeemable Convertible Stock
Related Party Transaction [Line Items]
Warrant purchase price per share							$ 11.52
Common Stock
Related Party Transaction [Line Items]
Warrant purchase price per share							$ 0.79
Common Stock Warrant \| Series C Redeemable Convertible Stock
Related Party Transaction [Line Items]
Warrant exercised						46,869
Sutro Biopharma, Inc
Related Party Transaction [Line Items]
Common stock, shares owned		1,600,000		1,600,000			1,600,000
Accrued expenses payable		$ 100		$ 100
Sutro Biopharma, Inc \| Maximum
Related Party Transaction [Line Items]
Accrued expenses payable							$ 100
Sutro Biopharma, Inc \| License Agreement
Related Party Transaction [Line Items]
Percentage of royalty payment on annual net sales of vaccine products for human health		4.00%		4.00%
Percentage of royalty payment on net sales of vaccine compositions for animal health		2.00%		2.00%
Sutro Biopharma, Inc \| Supply Agreement
Related Party Transaction [Line Items]
Change in fair value of redeemable convertible preferred stock warrant		$ 100	$ 1,000	$ 300	1,100
Sutro Biopharma, Inc \| Series C Redeemable Convertible Stock
Related Party Transaction [Line Items]
Warrant to purchase shares of stock							59,276
Warrant purchase price per share							$ 11.5215
Sutro Biopharma, Inc \| Series C Redeemable Convertible Stock \| License Amendment A2
Related Party Transaction [Line Items]
Warrant to purchase shares of stock	59,276
Warrant purchase price per share	$ 11.5215
Warrant exercisable and vests immediately and expires date	May 29, 2018
Sutro Biopharma, Inc \| Common Stock
Related Party Transaction [Line Items]
Warrant to purchase shares of stock							31,857
Warrant purchase price per share							$ 0.79289
Sutro Biopharma, Inc \| Common Stock Warrant
Related Party Transaction [Line Items]
Warrant exercised							30,278
Sutro Biopharma, Inc \| Preferred Stock Warrant
Related Party Transaction [Line Items]
Warrant exercised							16,591
Change in fair value of redeemable convertible preferred stock warrant		$ 0		$ 200
Sutro Biopharma, Inc \| Preferred Stock Warrant \| Maximum
Related Party Transaction [Line Items]
Change in fair value of redeemable convertible preferred stock warrant			$ 100		$ 100