Icosavax (ICVX) 10-Q 15 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 12, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Entity Registrant Name	ICOSAVAX, INC.
Entity Central Index Key	0001786255
Entity File Number	001-40655
Entity Tax Identification Number	82-3640549
Entity Current Reporting Status	No
Entity Shell Company	false
Entity Filer Category	Non-accelerated Filer
Entity Interactive Data Current	Yes
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Address Address Line1	1616 Eastlake Avenue E.
Entity Address, Address Line Two	Suite 208
Entity Address City Or Town	Seattle
Entity Address, State and Province	WA
Entity Incorporation State Country Code	DE
Entity Address Postal Zip Code	98102
Local Phone Number	737-0085
City Area Code	206
Security12b Title	Common Stock, $0.0001 par value per share
Trading Symbol	ICVX
Security Exchange Name	NASDAQ
Entity Common Stock, Shares Outstanding		39,041,805

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash	$ 291,271	$ 13,114
Restricted cash	2,652	2,384
Prepaid expenses and other current assets	6,353	662
Total current assets	300,276	16,160
Property and equipment, net	548	10
Total assets	300,824	16,170
Current liabilities:
Accounts payable	3,049	1,918
Accrued and other current liabilities	2,487	1,532
Deferred revenue	2,652	2,384
Total current liabilities	8,188	5,834
Long-term convertible promissory note		4,947
Embedded derivative liability		1,604
Other noncurrent liabilities	197	426
Total liabilities	8,385	12,811
Commitments and contingencies (Note 2)
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 50,000,000 and no shares authorized at September 30, 2021 and December 31, 2020, respectively; no shares issued and outstanding at September 30, 2021 and December 31, 2020	0	0
Common stock, $0.0001 par value; 500,000,000 and 78,000,000 shares authorized at September 30, 2021 and December 31, 2020, respectively; 38,588,648 and 3,596,936 shares issued at September 30, 2021 and December 31, 2020, respectively; 38,991,403 and 2,639,026 shares outstanding at September 30, 2021 and December 31, 2020, respectively	5	2
Additional paid-in capital	368,321	393
Accumulated deficit	(75,887)	(27,098)
Total stockholders' equity (deficit)	292,439	(26,703)
Total liabilities, convertible preferred stock and stockholders' equity (deficit)	$ 300,824	16,170
Convertible Preferred Stock [Member]
Current liabilities:
Convertible preferred stock, $0.0001 par value; no shares authorized at September 30, 2021 and 54,039,749 shares authorized at December 31, 2020; no shares issued and outstanding at September 30, 2021 and 32,198,879 shares issued and outstanding at December 31, 2020; $0 and $30,007 aggregate liquidation preference at September 30, 2021 and December 31, 2020, respectively		$ 30,062

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Aug. 02, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Aug. 31, 2018	Dec. 31, 2017
Convertible preferred stock, aggregate liquidation preference	$ 0				$ 30,007
Preferred stock, par value	$ 0.0001				$ 0.0001
Preferred stock, shares authorized	50,000,000	50,000,000			0
Preferred stock, shares issued	0				0
Preferred stock, shares outstanding	0				0
Common stock, par value	$ 0.0001				$ 0.0001
Common stock, shares authorized	500,000,000	500,000,000			78,000,000
Common stock, shares issued	39,387,389				3,596,936					192,276	77,418
Common Stock Shares Outstanding	38,991,403				2,639,026
Convertible Preferred Stock [Member]
Convertible preferred stock, par value	$ 0.0001				$ 0.0001
Convertible preferred stock, shares authorized	0				54,039,749
Convertible preferred stock, shares issued	0				32,198,879
Convertible preferred stock, shares outstanding	0		89,908,215	89,908,215	32,198,879	32,198,879	32,198,879	32,198,879	32,198,879
Preferred stock, par value				$ 0.0001

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Grant revenue	$ 1,827	$ 0	$ 5,732	$ 0
Operating expenses:
Research and development	10,883	4,752	24,713	12,338
General and administrative	25,357	704	28,669	1,857
Total operating expenses	36,240	5,456	53,382	14,195
Loss from operations	(34,413)	(5,456)	(47,650)	(14,195)
Other income (expense):
Change in fair value of embedded derivative liability			(205)	(1,791)
Loss on extinguishment of convertible promissory note	0	0	(754)	0
Interest and other income (expense)	27	(121)	(180)	(51)
Total other income (expense)	27	(121)	(1,139)	(51)
Net loss and comprehensive loss	$ (34,386)	$ (5,577)	$ (48,789)	$ (14,246)
Net loss per share, basic and diluted	$ (1.30)	$ (2.40)	$ (4.50)	$ (6.66)
Weighted-average common shares outstanding, basic and diluted	26,494,914	2,321,765	10,836,894	2,139,768

Condensed Statements of Convert

Condensed Statements of Convertible Preferred Stock and Stockholder's Deficit (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid In Capital [Member]	Accumulated Deficit [Member]	Convertible Preferred Stock [Member]	Convertible Preferred Stock [Member]Series A1 Convertible Preferred Stock [Member]	Convertible Preferred Stock [Member]Series B1 Convertible Preferred Stock [Member]
Beginning Balance at Dec. 31, 2019	$ (8,243)	$ 1		$ (8,244)
Beginning Balance (in shares) at Dec. 31, 2019		1,901,656
Convertible preferred stock, Beginning Balance at Dec. 31, 2019					$ 30,062
Convertible preferred stock, Beginning Balance (in shares) at Dec. 31, 2019					32,198,879
Shares released from restriction upon vesting of early-exercised stock options	1		$ 1
Shares released from restriction upon vesting of early-exercised stock options (in shares)		25,641
Vesting of shares of restricted common stock (in Shares)		117,369
Stock-based compensation	54		54
Net loss and comprehensive loss	(3,471)			(3,471)
Ending Balance at Mar. 31, 2020	(11,659)	$ 1	55	(11,715)
Ending Balance (in shares) at Mar. 31, 2020		2,044,666
Convertible preferred stock, Ending Balance at Mar. 31, 2020					$ 30,062
Convertible preferred stock, Ending Balance (in shares) at Mar. 31, 2020					32,198,879
Beginning Balance at Dec. 31, 2019	(8,243)	$ 1		(8,244)
Beginning Balance (in shares) at Dec. 31, 2019		1,901,656
Convertible preferred stock, Beginning Balance at Dec. 31, 2019					$ 30,062
Convertible preferred stock, Beginning Balance (in shares) at Dec. 31, 2019					32,198,879
Net loss and comprehensive loss	(14,246)
Ending Balance at Sep. 30, 2020	(22,192)	$ 2	296	(22,490)
Ending Balance (in shares) at Sep. 30, 2020		2,287,775
Convertible preferred stock, Ending Balance at Sep. 30, 2020					$ 30,062
Convertible preferred stock, Ending Balance (in shares) at Sep. 30, 2020					32,198,879
Beginning Balance at Mar. 31, 2020	(11,659)	$ 1	55	(11,715)
Beginning Balance (in shares) at Mar. 31, 2020		2,044,666
Convertible preferred stock, Beginning Balance at Mar. 31, 2020					$ 30,062
Convertible preferred stock, Beginning Balance (in shares) at Mar. 31, 2020					32,198,879
Stock-based compensation	63		63
Net loss and comprehensive loss	(5,198)			(5,198)
Ending Balance at Jun. 30, 2020	(16,794)	$ 1	118	(16,913)
Ending Balance (in shares) at Jun. 30, 2020		2,044,666
Convertible preferred stock, Ending Balance at Jun. 30, 2020					$ 30,062
Convertible preferred stock, Ending Balance (in shares) at Jun. 30, 2020					32,198,879
Shares released from restriction upon vesting of early-exercised stock options	109	$ 1	108
Shares released from restriction upon vesting of early-exercised stock options (in shares)		117,381
Vesting of shares of restricted common stock (in Shares)		125,728
Stock-based compensation	70		70
Net loss and comprehensive loss	(5,577)			(5,577)
Ending Balance at Sep. 30, 2020	(22,192)	$ 2	296	(22,490)
Ending Balance (in shares) at Sep. 30, 2020		2,287,775
Convertible preferred stock, Ending Balance at Sep. 30, 2020					$ 30,062
Convertible preferred stock, Ending Balance (in shares) at Sep. 30, 2020					32,198,879
Beginning Balance at Dec. 31, 2020	(26,703)	$ 2	393	(27,098)
Beginning Balance (in shares) at Dec. 31, 2020		2,639,026
Convertible preferred stock, Beginning Balance at Dec. 31, 2020					$ 30,062
Convertible preferred stock, Beginning Balance (in shares) at Dec. 31, 2020					32,198,879
Issuance of Series convertible preferred stock						$ 21,005	$ 92,654
Issuance of Series convertible preferred stock, (in shares)						21,944,874	32,958,612
Issuance of Series B-2 convertible preferred stock from convertible note					$ 7,917
Issuance of Series B-2 convertible preferred stock from convertible note (in shares)					2,805,850
Shares released from restriction upon vesting of early-exercised stock options	63		63
Shares released from restriction upon vesting of early-exercised stock options (in shares)		100,238
Exercise of common stock options	29		29
Exercise of common stock options, (in shares)		35,143
Vesting of shares of restricted common stock (in Shares)		117,369
Stock-based compensation	276		276
Net loss and comprehensive loss	(5,851)			(5,851)
Ending Balance at Mar. 31, 2021	(32,186)	$ 2	761	(32,949)
Ending Balance (in shares) at Mar. 31, 2021		2,891,776
Convertible preferred stock, Ending Balance at Mar. 31, 2021					$ 151,638
Convertible preferred stock, Ending Balance (in shares) at Mar. 31, 2021					89,908,215
Beginning Balance at Dec. 31, 2020	$ (26,703)	$ 2	393	(27,098)
Beginning Balance (in shares) at Dec. 31, 2020		2,639,026
Convertible preferred stock, Beginning Balance at Dec. 31, 2020					$ 30,062
Convertible preferred stock, Beginning Balance (in shares) at Dec. 31, 2020					32,198,879
Exercise of common stock options, (in shares)	202,223
Net loss and comprehensive loss	$ (48,789)
Ending Balance at Sep. 30, 2021	292,439	$ 5	368,321	(75,887)
Ending Balance (in shares) at Sep. 30, 2021		38,991,403
Convertible preferred stock, Ending Balance (in shares) at Sep. 30, 2021					0
Beginning Balance at Mar. 31, 2021	(32,186)	$ 2	761	(32,949)
Beginning Balance (in shares) at Mar. 31, 2021		2,891,776
Convertible preferred stock, Beginning Balance at Mar. 31, 2021					$ 151,638
Convertible preferred stock, Beginning Balance (in shares) at Mar. 31, 2021					89,908,215
Issuance costs incurred related to convertible preferred stock					$ (1)		$ (24)
Shares released from restriction upon vesting of early-exercised stock options	32		32
Shares released from restriction upon vesting of early-exercised stock options (in shares)		63,257
Vesting of shares of restricted common stock (in Shares)		117,369
Stock-based compensation	1,408		1,408
Net loss and comprehensive loss	(8,552)			(8,552)
Ending Balance at Jun. 30, 2021	(39,298)	$ 2	2,201	(41,501)
Ending Balance (in shares) at Jun. 30, 2021		3,072,402
Convertible preferred stock, Ending Balance at Jun. 30, 2021					$ 151,613
Convertible preferred stock, Ending Balance (in shares) at Jun. 30, 2021					89,908,215
Shares released from restriction upon vesting of early-exercised stock options	82		82
Shares released from restriction upon vesting of early-exercised stock options (in shares)		124,536
Exercise of common stock options	48		48
Exercise of common stock options, (in shares)		57,492
Vesting of shares of restricted common stock (in Shares)		148,743
Initial public offering, net of issuance costs	190,710	$ 1	190,709
Initial public offering, net of issuance costs, (in Shares)		13,953,332
Conversion of convertible preferred stock into common stock	151,613	$ 2	151,611		$ (151,613)
Conversion of convertible preferred stock into common stock, shares		21,634,898			(89,908,215)
Stock-based compensation	23,670		23,670
Net loss and comprehensive loss	(34,386)			(34,386)
Ending Balance at Sep. 30, 2021	$ 292,439	$ 5	$ 368,321	$ (75,887)
Ending Balance (in shares) at Sep. 30, 2021		38,991,403
Convertible preferred stock, Ending Balance (in shares) at Sep. 30, 2021					0

Condensed Statements of Conve_2

Condensed Statements of Convertible Preferred Stock and Stockholder's Deficit (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2021	Mar. 31, 2021
IPO [Member]
Issuance costs	$ 18.6
Series A1 Convertible Preferred Stock
Convertible preferred stock issuance cost, per share		$ 0.9615
Convertible preferred stock issuance cost, net		$ 0.1
Series B1 Convertible Preferred Stock
Convertible preferred stock issuance cost, per share		$ 2.82172
Convertible preferred stock issuance cost, net		$ 0.3

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities:
Net loss	$ (48,789)	$ (14,246)
Adjustments to reconcile net loss to cash used in operating activities:
Stock-based compensation	25,354	187
Depreciation	46	0
Non-cash interest expense	264	0
Change in fair value of embedded derivative liability	205	1,791
Loss on extinguishment of convertible promissory note	754	0
Changes in operating assets and liabilities:
Prepaids and other current assets	(5,691)	(294)
Accounts payable	1,130	590
Accrued & other current liabilities	955	1,452
Deferred revenue	268	0
Net cash used in operating activities	(25,504)	(10,520)
Investing activities:
Purchases of property and equipment	(583)	(10)
Net cash used in investing activities	(583)	(10)
Financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs	113,634	4,756
Proceeds from initial public offering, net of offering costs	190,710	0
Proceeds from exercise of stock options, including early exercise	168	172
Net cash provided by financing activities	304,512	4,928
Net increase (decrease) in cash and restricted cash	278,425	(5,602)
Cash and restricted cash at beginning of period	15,498	23,079
Cash and restricted cash at end of period	293,923	17,477
Supplemental disclosure of noncash activities
Conversion of preferred stock to common stock	151,613	0
Purchases of property and equipment included in accounts payable	$ 15	$ 0

Description of Business

Description of Business	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	1. Description of Business Organization Icosavax, Inc. (the “Company”) was incorporated in the state of Delaware on November 1, 2017, and is located in Seattle, Washington. The Company is focused on the research and development of vaccines against infectious diseases. The Company was founded on computationally designed virus-like particle technology, exclusively licensed for a variety of infectious disease indications from the Institute for Protein Design at the University of Washington. The Company’s business involves inherent risks. These risks include, among others, dependence on key personnel, licensors and third-party service providers, patentability of the Company’s products and processes, and clinical efficacy of the Company’s products under development. In addition, any of the technologies covering the Company’s existing products under development could become obsolete or diminished in value by discoveries and developments at other organizations. In July 2021, the Company effected a 1-for-4.1557 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of the Company’s convertible preferred stock. Accordingly, all share and per share amounts for all periods presented in the accompanying condensed financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split and adjustment of the convertible preferred stock conversion ratios. On August 2, 2021, the Company completed its initial public offering (“IPO” ) pursuant through which it issued 12,133,333 shares of its common stock at a public offering price of $ 15.00 per share, and on August 2, 2021, the Company sold an additional 1,819,999 shares pursuant to the exercise by the underwriters of their option to purchase additional shares. The Company received net proceeds from its IPO, inclusive of the exercise by the underwriters of their option to purchase additional shares, of $ 190.7 million, after deducting underwriting discounts and commissions and offering expenses. Upon the closing of the IPO, all 89,908,215 shares of the then outstanding convertible preferred stock automatically converted into 21,634,898 shares of common stock. Liquidity The Company had an accumulated deficit of $ 75.9 million, cash of $ 291.3 million, and restricted cash of $ 2.7 million at September 30, 2021. Management believes the Company has sufficient capital to execute its strategic plan and fund operations through at least the next twelve months from the date these condensed financial statements are issued. The Company has devoted substantially all of its resources to organizing and staffing the Company, business planning, raising capital, in-licensing intellectual property rights, developing vaccine candidates, scaling up manufacturing of vaccine candidates, and preparing for its ongoing and planned preclinical studies and clinical trials. The Company has a limited operating history, and the sales and income potential of its business is unproven. The Company has incurred net losses and negative cash flows from operating activities since its inception and expects to continue to incur net losses into the foreseeable future as it continues the development of its vaccine candidates. From inception to September 30, 2021, the Company has funded its operations primarily through the sale of its convertible preferred stock and common stock. On August 2, 2021, the Company completed its IPO and received net proceeds of $ 190.7 million. As the Company continues to pursue its business plan, it expects to finance its operations through equity offerings, debt financings or other capital sources, including potential strategic collaborations, licenses, and other similar arrangements. However, there can be no assurance that any additional financing or strategic transactions will be available to the Company on acceptable terms, if at all. If events or circumstances occur such that the Company does not obtain additional funding, it may need to delay, reduce or eliminate its product development or future commercialization efforts, which could have a material adverse effect on the Company’s business, results of operations or financial condition. The accompanying financial statements do not include any adjustments that might be necessary if the Company were unable to continue as a going concern.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited condensed financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 have been prepared in conformity with generally accepted accounting principles (“GAAP”) in the United States of America for interim financial information and pursuant to Article 10 of Regulation S-X of the Securities Act of 1933, as amended (the “Securities Act”). Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. These unaudited condensed financial statements include only normal and recurring adjustments that the Company believes are necessary to fairly state the Company’s financial position and the results of its operations and cash flows. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of the results expected for the full fiscal year or any subsequent interim period. The condensed balance sheet at December 31, 2020 has been derived from the audited financial statements at that date but does not include all disclosures required by GAAP for complete financial statements. Because all of the disclosures required by GAAP for complete financial statements are not included herein, these unaudited condensed financial statements and the notes accompanying them should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2020 included in the Company’s final prospectus for its IPO filed pursuant to Rule 424(b)(4) under the Securities Act, with the Securities and Exchange Commission (the “SEC”) on July 22, 2021. Use of Estimates The Company’s significant accounting policies are described in Note 2, “Summary of significant accounting policies,” of the Company’s audited financial statements for the year ended December 31, 2020 included in the Company’s final prospectus for its IPO filed with the SEC. There have been no material changes to the significant accounting policies previously disclosed in those audited financial statements. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses, clinical trials and research and development costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain or treat COVID-19, as well as the economic impact on local, regional, national and international markets. The Company has considered potential impacts arising from the COVID-19 pandemic and is not presently aware of any events or circumstances that would require the Company to update its estimates, judgments or revise the carrying value of its assets or liabilities. Fair Value of Financial Instruments The accounting guidance defines fair value, establishes a consistent framework for measuring fair value, and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The carrying amounts of all cash, restricted cash, prepaid expenses and other assets, accounts payable, and accrued and other current liabilities are considered to be representative of their respective fair values due to their short maturities. Derivative Liability, Convertible Notes Discount and Amortization The Company’s convertible note (see Note 7) had conversion and redemption features that met the definition of an embedded derivative and were therefore subject to bifurcation and derivative accounting. The initial recognition of the fair value of the derivative resulted in a discount to the convertible note, with a corresponding derivative liability. The discount to the convertible note was amortized using the effective interest method. The amortization of the discount is included in interest and other income (expense) in the statements of operations and comprehensive loss. The derivative liability related to these features was recorded at estimated fair value and remeasured on a recurring basis. Any changes in fair value were reflected as change in fair value of derivative liability in the statements of operations and comprehensive loss at each reporting date while such instruments were outstanding. The derivative liability was settled in March 2021 upon conversion of the underlying convertible note into Series B convertible preferred stock, resulting in a loss on extinguishment of convertible promissory note. Liability for Early Exercise of Stock Options Certain individuals were granted the ability to early exercise their stock options. The shares of common stock issued from the early exercise of unvested stock options are restricted and continue to vest in accordance with the original vesting schedule. The Company has the option to repurchase any unvested shares at the original purchase price upon any voluntary or involuntary termination. The shares purchased by the employees and non-employees pursuant to the early exercise of stock options are not deemed, for accounting purposes, to be outstanding until those shares vest. The cash received in exchange for exercised and unvested shares related to stock options granted is recorded as a liability for the early exercise of stock options on the accompanying balance sheets and will be reclassified as common stock and additional paid-in capital as the shares vest. Unvested shares issued under early exercise provisions subject to repurchase by the Company totaled 316,736 and 488,226 shares as of September 30, 2021 and December 31, 2020, respectively. As of September 30, 2021 and December 31, 2020, the Company recorded $ 0.2 million and $ 0.2 million respectively, associated with shares issued with repurchase rights as other noncurrent liabilities in the accompanying condensed balance sheets. Commitments and Contingencies The Company recognizes a liability with regard to loss contingencies when it believes it is probable a liability has been incurred, and the amount can be reasonably estimated. If some amount within a range of loss appears at the time to be a better estimate than any other amount within the range, the Company accrues that amount. When no amount within the range is a better estimate than any other amount the Company accrues the minimum amount in the range. In the event the Company becomes subject to claims or suits arising in the ordinary course of business, the Company would accrue a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. The Company has not recorded any such liabilities at either September 30, 2021 or December 31, 2020. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted- average number of shares of common stock outstanding for the period. Diluted net loss per share is computed by dividing the net loss by the weighted average number of shares of common stock and common stock equivalents outstanding for the period. Common stock equivalents are only included when their effect is dilutive. The Company’s potentially dilutive securities include outstanding stock options under the Company’s equity incentive plan and have been excluded from the computation of diluted net loss per share as they would be anti-dilutive to the net loss per share. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. The following tables summarize the computation of the basic and diluted net loss per share (in thousands, except share and per share data): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Numerator: Net loss $ ( 34,386 ) $ ( 5,577 ) $ ( 48,789 ) $ ( 14,246 ) Denominator: Weighted-average common shares outstanding, basic and 27,005,750 3,539,644 11,559,311 3,489,750 Less: Weighted average unvested common stock ( 510,836 ) ( 1,217,879 ) ( 722,417 ) ( 1,349,982 ) Weighted average shares used to compute net loss per 26,494,914 2,321,765 10,836,894 2,139,768 Net loss per share, basic and diluted $ ( 1.30 ) $ ( 2.40 ) $ ( 4.50 ) $ ( 6.66 ) The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because their inclusion would be anti-dilutive. As of September 30, 2021 2020 Series A convertible preferred stock - 32,198,879 Common stock options 6,365,633 439,203 Unvested common stock 402,755 1,217,710 Total 6,768,388 33,855,792 Segments The Company has determined that it operates and manages one operating segment, which is the business of researching and developing vaccines against infectious diseases. The Company’s chief operating decision maker, its chief executive officer, reviews financial information on an aggregate basis for the purpose of allocating resources. All assets of the Company are located in the United States. Recent Accounting Pronouncements Recently Adopted Accounting Standards In December 2019, the FASB issued ASU 2019-12, Income Taxes—Simplifying the Accounting for Income Taxes (“ASU 2019-12”). The new guidance simplifies the accounting for income taxes by removing several exceptions in the current standard and adding guidance to reduce complexity in certain areas, such as requiring that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. The new standard is effective for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022 for all non-public entities, with early adoption permitted, and is effective for fiscal years beginning after December 15, 2020, including interim periods within those annual periods for public entities. Early adoption is permitted. The Company adopted ASU 2019-12 on January 1, 2021 and the standard did not have a material impact on its condensed financial statements and related disclosures. There were no other significant updates to the recently issued accounting standards other than as disclosed herewith for the three and nine months ended September 30, 2021. Although there are several other new accounting pronouncements issued or proposed by the FASB, the Company does not believe any of those accounting pronouncements have had or will have a material impact on its financial position or operating results.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1 —Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities. Level 2 —Quoted prices for similar assets and liabilities in active markets, quoted prices in markets that are not active, or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability. Level 3 —Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e. supported by little or no market activity). No transfers between levels have occurred during the periods presented. The following table summarizes financial liabilities that the Company measured at fair value on a recurring basis, classified in accordance with the fair value hierarchy (in thousands): Fair Value Measurements at Report Date Using Total (Level 1) (Level 2) (Level 3) As of December 31, 2020 Embedded derivative liability $ ( 1,604 ) $ — $ — $ ( 1,604 ) There were no assets or liabilities measured at fair value on a recurring basis as of September 30, 2021. As further described in Note 7, the Company issued a convertible promissory note in August 2020. The convertible promissory note contained certain features that met the definition of a derivative and were required to be bifurcated. The Company has accounted for these as a single derivative comprising all the features requiring bifurcation. The fair value of the derivative liability was estimated using a scenario-based analysis comparing the probability-weighted present value of the convertible promissory note payoff at maturity with and without the bifurcated features. The Company considered possible outcomes available to the noteholders, including various financing dissolution scenarios. In addition, the probabilities applied to various scenarios, the key unobservable inputs are the time to liquidity for each scenario, and the discount rate. The following table summarizes information about the significant unobservable inputs used in the fair value measurements for the derivative liability: March 19, 2021 Probability of financing 100 % Probability of dissolution 0 % Time to liquidity (years) 0 % Discount rate 7.6 % The Company adjusted the carrying value of the derivative liability within the convertible promissory note to the estimated fair value at each reporting date, with any related increases or decreases in the fair value recorded as change in fair value of derivative liability in the statements of operations and comprehensive loss. For the three and nine months ended September 30, 2020, there was no change in the fair value of the derivative liability recognized in the statements of operations and comprehensive loss. For the three and nine months ended September 30, 2021 the Company recognized $ 0 and $ 0.2 million , respectively, of other expense in the statements of operations and comprehensive loss related to increases in the fair value of the derivative liability. On March 19, 2021, in connection with the closing of the Series B convertible preferred stock financing, the convertible promissory note (including accrued interest) and derivative liability converted into 2,805,850 shares of Series B-2 convertible preferred stock. As a result of the conversion, the Company recorded a loss on extinguishment of convertible promissory notes of $ 0.8 million in other expense in the condensed statements of operations and comprehensive loss for the nine months ended September 30, 2021, which included the write off of unamortized debt issuance costs. The following table provides a reconciliation of the fair value of the derivative liability using Level 3 significant unobservable inputs (in thousands): Convertible Promissory Note Fair value at December 31, 2020 $ ( 1,604 ) Change in fair value of embedded derivative liability ( 205 ) Reclassification of derivative liability into convertible preferred stock 1,809 Fair value at September 30, 2021 $ —

Grant Agreement

Grant Agreement	9 Months Ended
	Sep. 30, 2021
Grant Agreement [Abstract]
Grant Agreement	4. Grant Agreement Bill & Melinda Gates Foundation Grant Agreement In support of the Company’s development of a SARS-CoV-2 vaccine, in September 2020, the Company entered into the grant agreement (the “Grant Agreement”) with the Bill & Melinda Gates Foundation (“BMGF”), under which it was awarded a grant totaling up to $ 10.0 million (the “Grant”). The Grant supports development activities, including the Company’s regulatory filing preparations and planned Phase 1 clinical trial. Unless terminated earlier by BMGF, the Grant Agreement will continue in effect until March 31, 2022. The Company concurrently entered into a Global Access Commitments Agreement (“GACA”) with BMGF as part of the Grant Agreement. Under the terms of the GACA, among other things, the Company agreed to make a certain amount of a SARS-CoV-2 vaccine available and accessible at affordable pricing to people in certain low- and middle-income countries, if the vaccine is commercialized. Payments received in advance that are related to future performance are deferred and recognized as revenue when the research and development activities are performed. Cash payments received under the Grant Agreement are restricted as to their use until eligible expenditures are incurred. At both December 31, 2020 and September 30, 2021, the Company’s current restricted cash and deferred revenue balances on the condensed balance sheet represent funds received from BMGF and its estimate of costs to be reimbursed and revenue to be recognized, respectively, in the next twelve months under the Grant Agreement. During the three and nine months ended September 30, 2020, no funding had been received from BMGF. During the three and nine months ended September 30, 2021, the Company received $ 3.3 and $ 6.0 million, respectively from BMGF. During the three and nine months ended September 30, 2020, no revenue was recognized from the Grant Agreement. During the three and nine and months ended September 30, 2021, the Company recognized revenue from the Grant Agreement of $ 1.8 million and $ 5.7 million, respectively and has recognized approximately $ 7.3 million in revenue since the inception of the Grant Agreement. As of September 30, 2021, the Company has received the full $ 10.0 million under the Grant Agreement.

Accrued and Other Current Liabi

Accrued and Other Current Liabilities	9 Months Ended
	Sep. 30, 2021
Payables and Accruals [Abstract]
Accrued and Other Current Liabilities	5. Accrued and other current liabilities Accrued and other current liabilities consist of the following (in thousands): As of As of September 30, December 31, 2021 2020 Taxes payable $ - $ 91 Accrued paid time off 289 137 Accrued bonus 1,120 696 Other accrued liabilities 876 608 Accrued 401k 105 - ESPP liability 97 - Total accrued and other current liabilities $ 2,487 $ 1,532

License Agreements

License Agreements	9 Months Ended
	Sep. 30, 2021
License Agreements [Abstract]
License Agreements	6. License Agreements License Agreement with the National Institutes of Health On June 28, 2018, the Company entered into a non-exclusive patent license agreement (the “NIH Agreement”) with a U.S. government entity, the National Institutes of Health, represented by National Institute of Allergy and Infectious Disease (“NIAID”). The NIH Agreement was amended in September 2018 and September 2020. Under the NIH Agreement, the Company obtained a non-exclusive, worldwide, royalty-bearing, sublicensable license under certain NIAID patent rights, and transfer of know-how and biological materials for use in adjuvanted or non-adjuvanted vaccines for the prevention, cure, or treatment of RSV and metapneumovirus infection in humans. Under the NIH Agreement, the Company is required to use commercially reasonable efforts to meet certain specified development, sales and regulatory milestones related to the licensed products within specified time periods. In consideration of the rights granted to the Company under the NIH Agreement, the Company paid a licensing fee upon execution of the NIH Agreement of $ 100,000 , and will pay annual minimum royalty payments starting in the second year after the initial sale of each licensed product which can be credited against any earned royalties due for sales made in the year. There are milestone payments due upon the completion of certain development, regulatory, and commercial milestones for the licensed products in the future. The Company is obligated to pay aggregate potential milestone payments of up to $ 2.1 million with respect to future development and regulatory based milestones, and up to $ 6.5 million with respect to future sales milestones following commercialization. Additionally, the Company has agreed to pay a tiered royalty of a low single digit percentage on net sales of all products applicable to the license. Additional royalties would be due in connection with sublicenses. The Company’s royalty obligations continue for each licensed product for so long as licensed patent rights exist and have not expired, been revoked, lapsed, or held unenforceable. The NIH Agreement will terminate upon the last expiration of the patent rights or the Company may terminate the entirety of the agreement upon discontinuation of development or sales of licensed products and provision of written notice thereof to NIH. During the three and nine months ended September 30, 2020, the Company paid $ 0 in fees associated with the license and during the three and nine months ended September 30, 2021, the Company paid $ 0 and $ 25,000 , respectively, in fees associated with the license, which were recorded as research and development expenses. License Agreements with University of Washington On June 29, 2018, the Company entered into an agreement with an academic entity, the University of Washington (the “UW 2018 Agreement”), for an exclusive license to covered intellectual property for the prophylactic and/or therapeutic treatment of RSV infection and five other infectious diseases, a non-exclusive, worldwide license to use licensed know-how, and rights to sublicense. The licensed patents and know-how generally relate to computationally designed nanoparticles and vaccines based upon such designs, and relate to the Company’s proprietary two-component virus-like-particle technology. The UW 2018 Agreement was amended in June 2019 and again in November 2020. The Company’s rights and obligations under the UW 2018 Agreement are subject to certain U.S. government rights, certain global access commitment rights for humanitarian purposes to BMGF, certain rights to Howard Hughes Medical Institute, and certain other limited rights retained by University of Washington. The Company issued 192,276 shares of common stock on August 1, 2018 in exchange for the UW 2018 Agreement’s exclusive license. The shares issued were recorded at their estimated fair value, which is de minimis, with the related expense classified as research and development in 2018. Under the UW 2018 Agreement, the Company is required to use commercially reasonable efforts to meet certain specified development, sales and regulatory milestones related to the licensed products within specified time periods. In consideration of the rights granted to the Company under the UW 2018 Agreement, the Company is required to pay an annual maintenance fee in the mid four figures starting in 2020. Additionally, the Company is required to pay minimum annual royalties following the first year after commercial sale of each licensed product. There are milestone payments due upon the completion of certain development, regulatory, and commercial milestones for licensed products in the future. The aggregate potential milestone payments for future development, regulatory, and sales-based milestones are $ 1.4 million per indication, up to a maximum of $ 6.8 million in total milestone payments. Additionally, the Company has agreed to pay a royalty of a low single digit percentage on net sales of all licensed products. Additional royalties would be due in connection with sublicenses and milestones. The Company’s royalty obligations continue for each licensed product for so long as licensed patent rights exist and have not expired, been revoked, lapsed, or held unenforceable. The UW 2018 Agreement will terminate when all licensed rights have been terminated and all obligations due to the University of Washington have been fulfilled, or the Company may terminate the entirety of the agreement upon written notice thereof to the University of Washington. On July 2, 2020, the Company entered into a non-exclusive, worldwide (excluding South Korea) sublicensable license agreement with respect to specified intellectual property relating to the SARS-CoV-2 antigen with options for exclusivity in North America and Europe, subject to the performance of certain development milestones, with the University of Washington (the “UW 2020 Agreement”). The Company has since exercised its option for exclusivity in North America and Europe commencing in 2025. Under the UW 2020 Agreement, the Company also received a non-exclusive, worldwide license to use specific know-how and rights to sublicense for computationally designed nanoparticles and vaccines. The UW 2020 Agreement was amended in August 2020 and subsequently in May 2021. The Company’s rights and obligations under the UW 2020 Agreement as amended are subject to certain U.S. government rights, certain global access commitment rights for humanitarian purposes to BMGF, certain rights to Howard Hughes Medical Institute, and certain other limited rights retained by the University of Washington. Under the UW 2020 Agreement as amended, the Company is required to use commercially reasonable efforts to meet certain specified development, sales and regulatory milestones related to the licensed products within specified time periods. The Company has agreed to pay a royalty of a low single digit percentage on net sales of all products applicable to the license. However, the Company will not be required to pay royalties on net sales of any licensed product under the UW 2020 Agreement as amended if the Company is required to pay royalties on net sales under the UW 2018 Agreement. Additional royalties would be due in connection with sublicenses and milestones. The Company’s royalty obligations continue for each licensed product for so long as licensed patent rights exist and have not expired, been revoked, lapsed, or held unenforceable. The UW 2020 Agreement as amended will terminate when all licensed rights have been terminated and all obligations due to the University of Washington have been fulfilled, or the Company may terminate the entirety of the agreement upon written notice thereof to the University of Washington. During the three and nine months ended September 30, 2020, the Company paid $ 0.1 million and $ 0.1 million respectively, in fees associated with the 2018 and 2020 Agreements and during the three and nine months ended September 30, 2021, the Company paid $ 0.2 million and $ 0.3 million, respectively, in fees associated with the agreements. License Agreement with the University of Texas In June 2021, the Company entered into an exclusive patent license agreement with an academic entity, the University of Texas at Austin (the “UT Agreement”). Under the UT Agreement, the Company obtained an exclusive, worldwide, royalty-bearing, sublicensable license under certain patent rights, to use licensed know-how for prevention, cure, amelioration or treatment of respiratory disease caused by metapneumovirus infection in all vaccine fields, excluding mRNA-based vaccines. The Company is obligated to pay aggregate potential milestone payments of up to $ 0.8 million with respect to future development and regulatory based milestones, and up to $ 3.8 million with respect to future sales milestones following commercialization for each licensed product for so long as licensed patent rights exist and have not expired, been revoked, lapsed, or held unenforceable. The UT Agreement will terminate upon the last expiration of the patent rights or the Company may terminate the entirety of the agreement upon written notice thereof to the University of Texas at Austin. During the three and nine months ended September 30, 2021, the Company has no t incurred fees associated with the UT Agreement

Convertible Promissory Note

Convertible Promissory Note	9 Months Ended
	Sep. 30, 2021
Temporary Equity Disclosure [Abstract]
Convertible Promissory Note	7. Convertible Promissory Note In August 2020, the Company issued a $ 6.5 million convertible promissory note (“Convertible Promissory Note”). The Convertible Promissory Note accrued interest at a rate of 6 % a year with a maturity date two years from issuance. The Convertible Promissory Note could be converted or redeemed as follows (i) automatically converted in a qualified Series B financing transaction from which the Company would receive total gross proceeds of not less than $ 5.0 million at a conversion price equal to 85 % of the per share price paid by investors for such securities, (ii) automatically converted upon initial public offering at a conversion price equal to 85% of the per share price off common stock in the initial public offering, (iii) optionally converted into Series A-3 convertible preferred stock if a change in control, IPO, or qualified Series B financing had not occurred prior to the maturity date at a price equal to an amount determined by dividing $ 140 million by the fully diluted capitalization of the Company at the time of conversion, or (iv) repaid upon a change in control for an amount equal to the issue price plus accrued and unpaid interest or an amount as would have been payable if the noteholders had optionally converted into shares of Series A-3 convertible preferred stock. The Convertible Promissory Note was converted in March 2021 in connection with the Series B financing. The Convertible Promissory Note was accounted for in accordance with ASC 470-20, Debt with Conversion and Other Options (“ASC 470-20”) and ASC 815-15, Derivatives and Hedging - Embedded Derivatives (“ASC 815-15”). Under ASC 815-15, an embedded feature is required to be bifurcated if all three conditions are met: (1) economic characteristics and risks of the embedded derivative are not clearly and closely related to the economic characteristics and risks of the host contract, (2) the hybrid instrument is not remeasured at fair value under otherwise applicable GAAP with changes in fair value reported in earnings as they occur, and (3) a separate instrument which the same terms as the embedded derivative would be considered a derivative instrument subject to derivative accounting (the initial net investment for the hybrid instrument should not be considered to be the initial net investment for the embedded derivative). The Company bifurcated certain features that were required to be accounted for separately as a single embedded derivative. The initial fair value of this derivative of $ 1.8 million was recorded as a liability, and as a reduction to the carrying value of the Convertible Promissory Note. The Company also incurred approximately $ 36,000 of issuance costs related to the Convertible Promissory Note, which were also recorded as a reduction to the Convertible Promissory Note on the condensed balance sheet. The debt discount comprised of the initial fair value of the derivative liability and the issuance costs were amortized using the effective interest method over the two-year contractual term of the Convertible Promissory Note and presented as a direct reduction of the debt liability. The debt discount was being amortized at an effective interest rate of 23.8 %. Interest expense incurred in connection with the Convertible Promissory Note consisted of the following (in thousands): Nine Months Ended September 30, 2021 Coupon interest at 6% $ 86 Accretion of discount and amortization of issuance costs 177 Total interest expense on Convertible Promissory Note $ 263 The company incurred no interest expense related to the Convertible Promissory Note in the three months ended September 30, 2021. On March 19, 2021, in connection with the closing of the Series B convertible preferred stock financing, the Convertible Promissory Note (including accrued interest) and derivative liability converted into 2,805,850 shares of Series B-2 convertible preferred stock at an issuance price of $ 2.39846 per share. As a result of the conversion, the Company recorded a loss on extinguishment of convertible promissory notes of $ 0 and $ 0.8 million in other expense in the condensed statements of operations and comprehensive loss for the three and nine months ended September 30, 2021, respectively, which included the unamortized debt issuance costs.

Convertible Preferred Stock and

Convertible Preferred Stock and Stockholders' Equity (Deficit)	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity Note [Abstract]
Convertible Preferred Stock and Stockholders' Equity (Deficit)	8. Convertible Preferred Stock and Stockholders’ Equity (Deficit) Convertible Preferred Stock Prior to its conversion into common stock in connection with the Company’s IPO in August 2021, the Company’s convertible preferred stock was classified as temporary equity on the Company’s balance sheets in accordance with authoritative guidance. Convertible preferred stock authorized and issued and its principal terms as of December 31, 2020 consisted of the following ($ amounts in thousands): Share Shares Issued Shares of Aggregate Carry Series A-1 49,089,955 27,249,085 6,557,031 $ 26,200 $ 25,912 Series A-2 4,949,794 4,949,794 1,191,082 3,807 4,150 Total 54,039,749 32,198,879 7,748,113 $ 30,007 $ 30,062 In February 2021, the Company triggered a milestone closing associated with its Series A-1 convertible preferred stock resulting in the issuance of 21,944,874 shares. In March 2021, the Company entered into a convertible preferred stock purchase agreement for the issuance of 35,764,462 shares of Series B convertible preferred stock, $ 0.0001 par value per share, of which 32,958,612 shares of Series B-1 and 2,805,850 shares of Series B-2 were issued. In connection with the Company’s IPO in August 2021, all outstanding shares of the convertible preferred stock converted into 21,634,898 shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. There were no shares of convertible preferred stock outstanding as of the closing of the IPO. In addition, o n August 2, 2021, the Company amended and restated its certificate of incorporation to authorize 500,000,000 shares of common stock and 50,000,000 shares of preferred stock, which shares of preferred stock are currently undesignated. The Company does not have any outstanding preferred stock as of September 30, 2021. Equity Incentive Plans In 2017, the Company established a stock option plan (the “2017 Plan”) under which incentives may be granted to officers, employees, directors, consultants and advisors. Awards under the 2017 Plan may consist of restricted stock and incentive and non-qualified stock options to purchase shares of common stock of the Company. During 2021, the Company’s stockholders approved the 2021 Incentive Plan (the “2021 Plan”), which became effective in July 2021. The 2021 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock, dividend equivalents, restricted stock units and other stock or cash-based awards. The number of shares of the Company’s common stock initially reserved for issuance under the 2021 Plan is 4,600,000 shares; plus the shares of common stock remaining available for issuance under the 2017 Plan as of the effective date of the 2021 Plan, as well as any shares subject to outstanding awards under the 2017 Plan as of the effective date of the 2021 Plan that become available for issuance under the 2021 Plan thereafter in accordance with its terms. The number of shares initially available for issuance will be increased annually on January 1 of each calendar year beginning in 2022 and ending in and including 2031, equal to the lesser of (A) 5% of the shares outstanding on the final day of the immediately preceding calendar year and (B) a smaller number of shares as determined by our board of directors. No more than 50,000,000 shares of common stock may be issued under the 2021 Plan upon the exercise of incentive stock options The 2021 Plan is administered by the Board of Directors of the Company or a committee appointed by the Board of Directors, which determines the types of awards to be granted, including the number of shares subject to the awards, the exercise price and the vesting schedule. All existing grants are subject to a time-based vesting period which will generally be four years . Certain option and share awards provide for accelerated vesting if there is a change in control or if other contractually specified contingencies are met. The term of stock options granted under the 2021 Plan cannot exceed ten years (or five years in the case of incentive stock options granted to certain significant stockholders). Options shall not have an exercise price less than 100 % of the fair market value of the Company’s common stock on the grant date (or 110 % in the case of incentive stock options granted to certain significant stockholders), except with respect to certain substitute awards granted in connection with a corporate transaction. A summary of the status of the options issued under the Company's equity incentive plans as of September 30, 2021, and information with respect to the changes in options outstanding is as follows: Option Pool Options Weighted Average Exercise Weighted Average Remaining Aggregate Balance at December 31, 2020 541,411 641,427 $ 0.83 9.02 — Authorized increase in plan shares 22,634,965 — — — — Granted ( 5,982,133 ) 5,982,133 8.07 — — Exercised (including early) ( 202,223 ) 0.83 — $ 1,101,195 Balance at September 30, 2021 17,194,243 6,421,337 $ 7.57 9.17 $ 154,954,478 Vested and expected to vest as of September 30, 2021 6,421,337 $ 7.57 9.17 $ 154,954,478 Vested and exercisable at September 30, 2021 726,036 $ 5.09 9.29 $ 17,789,497 Exercisable options in the table above reflect the number of options vested as of the date reported. The 2021 plan permits early exercises of options. Cash received for early exercise of unvested options is carried as an other noncurrent liability in the accompanying condensed balance sheet and totaled $ 0.2 million at September 30, 2021. The aggregate intrinsic value in the table above is calculated as the difference between the exercise price of the underlying options and the estimate fair value of the Company’s common stock for all options that were in-the-money as of September 30, 2021. The weighted-average grant date fair value of option grants during the nine months ended September 30, 2021 was $ 8.07 per share. Common Stock In December 2017, the Company entered into restricted stock purchase agreements and issued 2,580,600 shares of restricted common stock to members of management, subject to repurchase by the Company. Any shares subject to repurchase by the Company are not deemed, for accounting purposes, to be outstanding until those shares vest. The management grants vested 20 % upon issuance and the remaining 80 % vest over 48 months in equal monthly installments. The grants provide for accelerated vesting upon a change in control or other contractually specified contingencies. In June 2018, 968,158 shares of the outstanding restricted shares were canceled, and the original proceeds were returned upon the departure of the founder. Given the early stage of the Company at the time of the grants, the value of all grants and the cash exchanged for the shares was de minimis. In December 2017 and August 2018, the Company issued 77,418 and 192,276 shares, respectively, of common stock to a university in connection with obtaining a licensing agreement. The shares issued to the university were fully vested upon issuance. As of September 30, 2021 and December 31, 2020, the Company had 2,347,629 shares of restricted common stock that had been issued to members of management at a price of $ 0.004 per share, and 269,694 shares of common stock that had been issued to a university in connection with obtaining a licensing agreement. At September 30, 2021 and December 31, 2020, 2,261,617 and 1,995,314 shares of the restricted common stock have vested, respectively. At September 30, 2021, 86,012 shares remain subject to vesting conditions and are expected to vest by December 2021. Common stock reserved for future issuance consisted of the following: As of September 30, 2021 Common stock options and restricted stock units granted and outstanding 6,421,337 Shares available for issuance under the equity incentive plans 8,383,215 Shares available for issuance under the 2021 Employee Stock Purchase Plan 1,200,000 Total common stock reserved for issuance 16,004,552 Stock-Based Compensation Expense Stock-based compensation expense for all equity awards has been reported in the condensed statements of operations and comprehensive loss as follows (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Research and development $ 931 $ 32 $ 1,471 $ 87 General and administrative 22,739 38 23,883 100 Total $ 23,670 $ 70 $ 25,354 $ 187 The Company recognizes compensation expense for options and restricted stock unit ("RSU") awards granted to employees and the board of directors based on their grant date fair value. During the three and nine months ended September 30, 2021, the Company granted 1,347,511 and 5,982,133 options, respectively, with a grant date fair value of $ 18.9 million and $ 44.4 million, respectively. During the three and nine months ended September 30, 2021, the Company granted 383,500 RSU awards, respectively, with a grant date fair value of $ 9.9 million. The compensation expense is recognized over the vesting period of 4 years on a straight-line basis. The fair value of each stock option granted was determined using the Black-Scholes option pricing model. The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee and nonemployee stock option grants issued during periods ended were as follows: Nine Months Ended 2021 2020 Risk-free rate of interest 0.53 %- 1.23 % 0.31 %- 1.40 % Expected term (years) 5.09 - 6.49 years 5.90 - 6.08 years Expected stock price volatility 86.0 %- 88.4 % 80.2 % - 86.4 % Dividend yield 0 % 0 % As of September 30, 2021, the unrecognized compensation cost related to outstanding stock options and RSU awards was $ 38.3 million and $ 9.5 million, respectively and is expected to be recognized as expense over a weighted-average period of approximately 3.63 years. On August 4, 2021, as a result of the death of Tadataka (Tachi) Yamada, M.D., the Company's former Chairman, the Company determined to accelerate the vesting of all of Dr. Yamada's previously unvested stock options as of the date of his death. The Company accelerated vesting on 611,639 shares, with exercise prices ranging from $ 0.83 to $ 5.90 per share, resulting in incremental non-cash, stock-based compensation expense of $ 21.0 million recorded during the three and nine months ended September 30, 2021. Employee Stock Purchase Plan During 2021, the Company’s stockholders approved the 2021 Employee Stock Purchase Plan (the “ESPP”), which became effective in July 2021. The number of shares of common stock initially reserved for issuance under the ESPP is 400,000 shares. The number of shares of common stock reserved for issuance under the ESPP will automatically increase on January 1, 2022 and each January 1 thereafter through January 1, 2031, in an amount equal to the lower of (1) 1 % of the aggregate number of shares of common stock of the Company outstanding on the final day of the immediately preceding calendar year and (2) such smaller number of shares of common stock as determined by the Board, provided that no more than 15,000,000 shares of our common stock may be issued under the ESPP. As of September 30, 2021, no shares have been purchased by employees under the ESPP. The first purchase under the ESPP is scheduled for December 2021.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes There was no provision for income taxes recorded during the three and nine months ended September 30, 2021 or 2020. The Company’s deferred tax assets continue to be reduced by a full valuation allowance. The Company is subject to income taxes in the United States and its effective tax rate is calculated quarterly based upon current assumptions relating to the full year’s estimated operating results and various tax-related items. Each quarter an estimate of the annual effective tax rate is updated should the Company revise its forecast of earnings based upon its operating results. If there is a change in the estimated effective annual tax rate, a cumulative adjustment is made. The Company's effective tax rate was 0 % for the three and nine months ended September 30, 2021 and 2020. The difference between the effective tax rate of 0 % and the U.S. federal statutory rate of 21 % for the three and nine months ended September 30, 2021 and 2020 was primarily due to recognizing a full valuation allowance on deferred tax assets. As of September 30, 2021, the Company determined that, based on an evaluation of the four sources of income and all available evidence, both positive and negative, including the Company's latest forecasts and cumulative losses in recent years, it was more likely than not that none of its deferred tax assets would be realized and therefore we continued to record a full valuation allowance. No current tax liability or expense has been recorded in the financial statements.

Employee Saving Plan

Employee Saving Plan	9 Months Ended
	Sep. 30, 2021
Postemployment Benefits [Abstract]
Employee Saving Plan	10. Employee Savings Plan The Company has a defined contribution 401(k) savings plan for those employees who meet minimum eligibility requirements. Under the terms of the plan, eligible employees may contribute up to 90 % of their annual compensation to the plan, subject to Internal Revenue Service limitations. The Company may also, at its sole discretion, make contributions to the plan. The Company did no t make any contributions to the plan during the three and nine months ended September 30, 2021 or 2020.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 have been prepared in conformity with generally accepted accounting principles (“GAAP”) in the United States of America for interim financial information and pursuant to Article 10 of Regulation S-X of the Securities Act of 1933, as amended (the “Securities Act”). Accordingly, they do not include all of the information and notes required by GAAP for complete financial statements. These unaudited condensed financial statements include only normal and recurring adjustments that the Company believes are necessary to fairly state the Company’s financial position and the results of its operations and cash flows. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of the results expected for the full fiscal year or any subsequent interim period. The condensed balance sheet at December 31, 2020 has been derived from the audited financial statements at that date but does not include all disclosures required by GAAP for complete financial statements. Because all of the disclosures required by GAAP for complete financial statements are not included herein, these unaudited condensed financial statements and the notes accompanying them should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2020 included in the Company’s final prospectus for its IPO filed pursuant to Rule 424(b)(4) under the Securities Act, with the Securities and Exchange Commission (the “SEC”) on July 22, 2021.
Use of Estimates	Use of Estimates The Company’s significant accounting policies are described in Note 2, “Summary of significant accounting policies,” of the Company’s audited financial statements for the year ended December 31, 2020 included in the Company’s final prospectus for its IPO filed with the SEC. There have been no material changes to the significant accounting policies previously disclosed in those audited financial statements. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses, clinical trials and research and development costs, will depend on future developments that are highly uncertain, including as a result of new information that may emerge concerning COVID-19 and the actions taken to contain or treat COVID-19, as well as the economic impact on local, regional, national and international markets. The Company has considered potential impacts arising from the COVID-19 pandemic and is not presently aware of any events or circumstances that would require the Company to update its estimates, judgments or revise the carrying value of its assets or liabilities.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The accounting guidance defines fair value, establishes a consistent framework for measuring fair value, and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The carrying amounts of all cash, restricted cash, prepaid expenses and other assets, accounts payable, and accrued and other current liabilities are considered to be representative of their respective fair values due to their short maturities.
Derivative Liability, Convertible Notes Discount and Amortization	Derivative Liability, Convertible Notes Discount and Amortization The Company’s convertible note (see Note 7) had conversion and redemption features that met the definition of an embedded derivative and were therefore subject to bifurcation and derivative accounting. The initial recognition of the fair value of the derivative resulted in a discount to the convertible note, with a corresponding derivative liability. The discount to the convertible note was amortized using the effective interest method. The amortization of the discount is included in interest and other income (expense) in the statements of operations and comprehensive loss. The derivative liability related to these features was recorded at estimated fair value and remeasured on a recurring basis. Any changes in fair value were reflected as change in fair value of derivative liability in the statements of operations and comprehensive loss at each reporting date while such instruments were outstanding. The derivative liability was settled in March 2021 upon conversion of the underlying convertible note into Series B convertible preferred stock, resulting in a loss on extinguishment of convertible promissory note.
Liability for Early Exercise of Stock Options	Liability for Early Exercise of Stock Options Certain individuals were granted the ability to early exercise their stock options. The shares of common stock issued from the early exercise of unvested stock options are restricted and continue to vest in accordance with the original vesting schedule. The Company has the option to repurchase any unvested shares at the original purchase price upon any voluntary or involuntary termination. The shares purchased by the employees and non-employees pursuant to the early exercise of stock options are not deemed, for accounting purposes, to be outstanding until those shares vest. The cash received in exchange for exercised and unvested shares related to stock options granted is recorded as a liability for the early exercise of stock options on the accompanying balance sheets and will be reclassified as common stock and additional paid-in capital as the shares vest. Unvested shares issued under early exercise provisions subject to repurchase by the Company totaled 316,736 and 488,226 shares as of September 30, 2021 and December 31, 2020, respectively. As of September 30, 2021 and December 31, 2020, the Company recorded $ 0.2 million and $ 0.2 million respectively, associated with shares issued with repurchase rights as other noncurrent liabilities in the accompanying condensed balance sheets.
Commitments and Contingencies	Commitments and Contingencies The Company recognizes a liability with regard to loss contingencies when it believes it is probable a liability has been incurred, and the amount can be reasonably estimated. If some amount within a range of loss appears at the time to be a better estimate than any other amount within the range, the Company accrues that amount. When no amount within the range is a better estimate than any other amount the Company accrues the minimum amount in the range. In the event the Company becomes subject to claims or suits arising in the ordinary course of business, the Company would accrue a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. The Company has not recorded any such liabilities at either September 30, 2021 or December 31, 2020.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted- average number of shares of common stock outstanding for the period. Diluted net loss per share is computed by dividing the net loss by the weighted average number of shares of common stock and common stock equivalents outstanding for the period. Common stock equivalents are only included when their effect is dilutive. The Company’s potentially dilutive securities include outstanding stock options under the Company’s equity incentive plan and have been excluded from the computation of diluted net loss per share as they would be anti-dilutive to the net loss per share. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. The following tables summarize the computation of the basic and diluted net loss per share (in thousands, except share and per share data): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Numerator: Net loss $ ( 34,386 ) $ ( 5,577 ) $ ( 48,789 ) $ ( 14,246 ) Denominator: Weighted-average common shares outstanding, basic and 27,005,750 3,539,644 11,559,311 3,489,750 Less: Weighted average unvested common stock ( 510,836 ) ( 1,217,879 ) ( 722,417 ) ( 1,349,982 ) Weighted average shares used to compute net loss per 26,494,914 2,321,765 10,836,894 2,139,768 Net loss per share, basic and diluted $ ( 1.30 ) $ ( 2.40 ) $ ( 4.50 ) $ ( 6.66 ) The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because their inclusion would be anti-dilutive. As of September 30, 2021 2020 Series A convertible preferred stock - 32,198,879 Common stock options 6,365,633 439,203 Unvested common stock 402,755 1,217,710 Total 6,768,388 33,855,792
Segments	Segments The Company has determined that it operates and manages one operating segment, which is the business of researching and developing vaccines against infectious diseases. The Company’s chief operating decision maker, its chief executive officer, reviews financial information on an aggregate basis for the purpose of allocating resources. All assets of the Company are located in the United States.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Recently Adopted Accounting Standards In December 2019, the FASB issued ASU 2019-12, Income Taxes—Simplifying the Accounting for Income Taxes (“ASU 2019-12”). The new guidance simplifies the accounting for income taxes by removing several exceptions in the current standard and adding guidance to reduce complexity in certain areas, such as requiring that an entity reflect the effect of an enacted change in tax laws or rates in the annual effective tax rate computation in the interim period that includes the enactment date. The new standard is effective for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022 for all non-public entities, with early adoption permitted, and is effective for fiscal years beginning after December 15, 2020, including interim periods within those annual periods for public entities. Early adoption is permitted. The Company adopted ASU 2019-12 on January 1, 2021 and the standard did not have a material impact on its condensed financial statements and related disclosures. There were no other significant updates to the recently issued accounting standards other than as disclosed herewith for the three and nine months ended September 30, 2021. Although there are several other new accounting pronouncements issued or proposed by the FASB, the Company does not believe any of those accounting pronouncements have had or will have a material impact on its financial position or operating results.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Computation of Basic and Diluted Net Loss Per Share	The following tables summarize the computation of the basic and diluted net loss per share (in thousands, except share and per share data): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Numerator: Net loss $ ( 34,386 ) $ ( 5,577 ) $ ( 48,789 ) $ ( 14,246 ) Denominator: Weighted-average common shares outstanding, basic and 27,005,750 3,539,644 11,559,311 3,489,750 Less: Weighted average unvested common stock ( 510,836 ) ( 1,217,879 ) ( 722,417 ) ( 1,349,982 ) Weighted average shares used to compute net loss per 26,494,914 2,321,765 10,836,894 2,139,768 Net loss per share, basic and diluted $ ( 1.30 ) $ ( 2.40 ) $ ( 4.50 ) $ ( 6.66 )
Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share	The following table sets forth the outstanding potentially dilutive securities that have been excluded in the calculation of diluted net loss per share because their inclusion would be anti-dilutive. As of September 30, 2021 2020 Series A convertible preferred stock - 32,198,879 Common stock options 6,365,633 439,203 Unvested common stock 402,755 1,217,710 Total 6,768,388 33,855,792

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value Liabilities Measured on Recurring Basis	The following table summarizes financial liabilities that the Company measured at fair value on a recurring basis, classified in accordance with the fair value hierarchy (in thousands): Fair Value Measurements at Report Date Using Total (Level 1) (Level 2) (Level 3) As of December 31, 2020 Embedded derivative liability $ ( 1,604 ) $ — $ — $ ( 1,604 )
Schedule of Significant Unobservable Inputs Used in the Fair Value Measurements for the Derivative Liability	The following table summarizes information about the significant unobservable inputs used in the fair value measurements for the derivative liability: March 19, 2021 Probability of financing 100 % Probability of dissolution 0 % Time to liquidity (years) 0 % Discount rate 7.6 %
Schedule of Reconciliation of the Fair Value of the Derivative Liability Using Level 3 Significant Unobservable Inputs	The following table provides a reconciliation of the fair value of the derivative liability using Level 3 significant unobservable inputs (in thousands): Convertible Promissory Note Fair value at December 31, 2020 $ ( 1,604 ) Change in fair value of embedded derivative liability ( 205 ) Reclassification of derivative liability into convertible preferred stock 1,809 Fair value at September 30, 2021 $ —

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Payables and Accruals [Abstract]
Schedule of Accrued and Other Current Liabilities	Accrued and other current liabilities consist of the following (in thousands): As of As of September 30, December 31, 2021 2020 Taxes payable $ - $ 91 Accrued paid time off 289 137 Accrued bonus 1,120 696 Other accrued liabilities 876 608 Accrued 401k 105 - ESPP liability 97 - Total accrued and other current liabilities $ 2,487 $ 1,532

Convertible Promissory Note (Ta

Convertible Promissory Note (Tables)	9 Months Ended
	Sep. 30, 2021
Convertible Promissory Note [Abstract]
Summary Of Interest Expense Of Convertible Promissory Note	Interest expense incurred in connection with the Convertible Promissory Note consisted of the following (in thousands): Nine Months Ended September 30, 2021 Coupon interest at 6% $ 86 Accretion of discount and amortization of issuance costs 177 Total interest expense on Convertible Promissory Note $ 263

Convertible Preferred Stock a_2

Convertible Preferred Stock and Stockholders' Equity (Deficit) (Tables)	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity Note [Abstract]
Schedule of Convertible Preferred Stock	Convertible preferred stock authorized and issued and its principal terms as of December 31, 2020 consisted of the following ($ amounts in thousands): Share Shares Issued Shares of Aggregate Carry Series A-1 49,089,955 27,249,085 6,557,031 $ 26,200 $ 25,912 Series A-2 4,949,794 4,949,794 1,191,082 3,807 4,150 Total 54,039,749 32,198,879 7,748,113 $ 30,007 $ 30,062
Summary of the Status of the Options Issued Under the Plan	A summary of the status of the options issued under the Company's equity incentive plans as of September 30, 2021, and information with respect to the changes in options outstanding is as follows: Option Pool Options Weighted Average Exercise Weighted Average Remaining Aggregate Balance at December 31, 2020 541,411 641,427 $ 0.83 9.02 — Authorized increase in plan shares 22,634,965 — — — — Granted ( 5,982,133 ) 5,982,133 8.07 — — Exercised (including early) ( 202,223 ) 0.83 — $ 1,101,195 Balance at September 30, 2021 17,194,243 6,421,337 $ 7.57 9.17 $ 154,954,478 Vested and expected to vest as of September 30, 2021 6,421,337 $ 7.57 9.17 $ 154,954,478 Vested and exercisable at September 30, 2021 726,036 $ 5.09 9.29 $ 17,789,497
Schedule of common stock reserved for future issuance	Common stock reserved for future issuance consisted of the following: As of September 30, 2021 Common stock options and restricted stock units granted and outstanding 6,421,337 Shares available for issuance under the equity incentive plans 8,383,215 Shares available for issuance under the 2021 Employee Stock Purchase Plan 1,200,000 Total common stock reserved for issuance 16,004,552
Schedule of Stock-based Compensation Expense for All Equity Awards	Stock-based compensation expense for all equity awards has been reported in the condensed statements of operations and comprehensive loss as follows (in thousands): Three Months Ended Nine Months Ended 2021 2020 2021 2020 Research and development $ 931 $ 32 $ 1,471 $ 87 General and administrative 22,739 38 23,883 100 Total $ 23,670 $ 70 $ 25,354 $ 187
Summary of Assumptions Used in Black-Scholes Model	The fair value of each stock option granted was determined using the Black-Scholes option pricing model. The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee and nonemployee stock option grants issued during periods ended were as follows: Nine Months Ended 2021 2020 Risk-free rate of interest 0.53 %- 1.23 % 0.31 %- 1.40 % Expected term (years) 5.09 - 6.49 years 5.90 - 6.08 years Expected stock price volatility 86.0 %- 88.4 % 80.2 % - 86.4 % Dividend yield 0 % 0 %

Description of Business - Addit

Description of Business - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Aug. 02, 2021	Aug. 31, 2021	Jul. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Aug. 31, 2018	Dec. 31, 2017
Subsidiary, Sale of Stock [Line Items]
Accumulated Deficit				$ 75,887		$ 27,098
Cash				291,271		$ 13,114
Restricted Cash				2,700
Proceeds from Issuance Initial Public Offering				$ 190,710	$ 0
Stock split			1-for-4.1557
Sale of common stock				39,387,389		3,596,936	192,276	77,418
Preferred stock, shares outstanding				0		0
IPO [Member]
Subsidiary, Sale of Stock [Line Items]
Proceeds from Issuance Initial Public Offering	$ 190,700
Sale of common stock	12,133,333
Offering price per share	$ 15
Additional shares purchasable by underwriters	1,819,999
Preferred stock, shares outstanding	89,908,215			0
Common stock converted	21,634,898	21,634,898

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2021USD ($)Segmentshares	Dec. 31, 2020USD ($)shares
Number of shares subject to repurchase | shares	316,736	488,226
Liabilities with shares issued with repurchase rights | $	$ 0.2	$ 0.2
Number Of Reporting Units | Segment	1

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss	$ (34,386)	$ (5,577)	$ (48,789)	$ (14,246)
Denominator:
Weighted-average common shares outstanding, basic and diluted	27,005,750	3,539,644	11,559,311	3,489,750
Less: Weighted average unvested common stock	(510,836)	(1,217,879)	(722,417)	(1,349,982)
Weighted average shares used to compute net loss per share, basic and diluted	26,494,914	2,321,765	10,836,894	2,139,768
Net loss per share, basic and diluted	$ (1.30)	$ (2.40)	$ (4.50)	$ (6.66)

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Securities Excluded in Calculation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive common equivalent shares	6,768,388	33,855,792
Common Stock [Member] | Stock Option [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive common equivalent shares	6,365,633	439,203
Unvested Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive common equivalent shares	402,755	1,217,710
Series A
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive common equivalent shares	0	32,198,879

Fair value measurements - Sched

Fair value measurements - Schedule of Fair Value Liabilities Measured on Recurring Basis (Details) $ in Thousands	Dec. 31, 2020USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liability	$ (1,604)
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liability	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liability	0
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Embedded derivative liability	$ (1,604)

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Mar. 19, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Change in fair value of derivative liability	$ 0		$ 0
Convertible preferred stock, Shares issued upon conversion						7,748,113
Loss on extinguishment of convertible promissory note	0	$ 0	(754,000)	$ 0
Series B-2 Convertible Preferred Stock [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Convertible preferred stock, Shares issued upon conversion					2,805,850
Operating Expense [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Increase in the fair value of the derivative liability	0		200,000
Operating Expense [Member] | Series B-2 Convertible Preferred Stock [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Loss on extinguishment of convertible promissory note			800,000
Fair Value, Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets measured at fair value	0		0
Liabilities measured at fair value	$ 0		$ 0

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Significant Unobservable Inputs Used in the Fair Value Measurements for the Derivative Liability (Details)	Mar. 19, 2021
Probability of financing
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative liability	100
Probability of dissolution
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative liability	0
Time to liquidity (years)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative liability	0
Discount rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative liability	7.6

Fair Value Measurements - Sch_3

Fair Value Measurements - Schedule of Reconciliation of the Fair Value of the Derivative Liability Using Level 3 Significant Unobservable Inputs (Details) - Level 3 $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Beginning balance	$ (1,604)
Change in fair value of embedded derivative liability	(205)
Reclassification of derivative liability into convertible stock resulting from conversion of convertible promissory note	1,809
Ending balance	$ 0

Grant Agreement - Additional In

Grant Agreement - Additional Information (Details) - BMGF Grant - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021
Grant Agreement [Line Items]
Grant received			$ 10,000,000
Funding received	$ 3,300,000	$ 0	6,000,000	$ 0
Revenue from grant	$ 1,800,000	$ 0	$ 5,700,000	$ 0	$ 7,300,000

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities - Schedule of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Taxes payable	$ 0	$ 91
Accrued paid time off	289	137
Accrued bonus	1,120	696
Other accrued liabilities	876	608
Accrued 401K	105	0
ESPP Liability	97	0
Accrued Liabilities, Current, Total	$ 2,487	$ 1,532

License Agreements - Additional

License Agreements - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Aug. 31, 2018	Aug. 01, 2018	Dec. 31, 2017
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sale of common stock	39,387,389		39,387,389		3,596,936	192,276		77,418
NIH Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of license fee			$ 100,000
Potential milestone payments			2,100,000
Potential milestone payments			6,500,000
NIH Agreement | Research and Development Expense [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of license fee	$ 0		25,000
NIH Agreement | License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of license fee		$ 0		$ 0
U W Two Thousand And Eighteen Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sale of common stock							192,276
Potential Payments for Future Development Regulatory and Sales Based Milestones			1,400,000
Total Milestone Payments			6,800,000
U W Two Thousand And Eighteen And U W Two Thousand And Twenty Agreement | License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of license fee	200,000	$ 100,000	300,000	$ 100,000
U T Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone payments			800,000
Potential milestone payments			3,800,000
U T Agreement | License
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Payment of license fee	$ 0		$ 0

Convertible Promissory Note - A

Convertible Promissory Note - Additional Information (Details) - USD ($)	Mar. 19, 2021	Aug. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021
Debt Conversion [Line Items]
Convertible promissory note issued		$ 6,500,000
Accrued interest rate, per annum		6.00%
Promissory note maturity period		2 years			2 years
Derivative Liability, Fair Value, Gross Liability			$ 1,800,000		$ 1,800,000
Payments of Debt Issuance Costs					36,000
Debt discount interest rate, effective percentage							23.80%
Loss on extinguishment of convertible promissory note			$ 0	$ 0	$ (754,000)	$ 0
Convertible Promissory Note
Debt Conversion [Line Items]
Debt Conversion, Converted Instrument, Amount		$ 140,000,000
Series A3 Convertible Preferred Stock | Convertible Promissory Note
Debt Conversion [Line Items]
Share price, percentage		85.00%
Series B-2 Convertible Preferred Stock [Member]
Debt Conversion [Line Items]
Promissory note and derivative liability conversion into share	2,805,850
Shares issued price per share	$ 2.39846
Minimum [Member] | Series A3 Convertible Preferred Stock | Convertible Promissory Note
Debt Conversion [Line Items]
Proceeds from Convertible Debt		$ 5,000,000

Convertible Promissory Note - S

Convertible Promissory Note - Summary of Interest Expense of Convertible Promissory Note (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Convertible Promissory Note [Abstract]
Coupon Interest at 6%	$ 86
Accretion of discount and amortization of issuance costs	177
Total interest expense on Convertible Promissory Note	$ 263

Convertible Preferred Stock a_3

Convertible Preferred Stock and Stockholders' Equity (Deficit) - Schedule of Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Share Authorized and Outstanding		54,039,749
Shares Issued and Outstanding		32,198,879
Convertible preferred stock, Shares issued upon conversion		7,748,113
Aggregate Liquidation Preference	$ 0	$ 30,007
Carry Value		$ 30,062
Series A-1
Class Of Stock [Line Items]
Share Authorized and Outstanding		49,089,955
Shares Issued and Outstanding		27,249,085
Convertible preferred stock, Shares issued upon conversion		6,557,031
Aggregate Liquidation Preference		$ 26,200
Carry Value		$ 25,912
Series A-2
Class Of Stock [Line Items]
Share Authorized and Outstanding		4,949,794
Shares Issued and Outstanding		4,949,794
Convertible preferred stock, Shares issued upon conversion		1,191,082
Aggregate Liquidation Preference		$ 3,807
Carry Value		$ 4,150

Convertible Preferred Stock a_4

Convertible Preferred Stock and Stockholders' Equity (Deficit) - Additional Information (Details) - USD ($)	Aug. 04, 2021	Aug. 02, 2021	Aug. 31, 2021	Jul. 31, 2021	Feb. 28, 2021	Aug. 31, 2020	Dec. 31, 2017	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Mar. 31, 2021	Aug. 31, 2018	Jun. 30, 2018
Class Of Stock [Line Items]
Common stock, shares authorized		500,000,000						500,000,000	500,000,000		78,000,000
Common stock, par value								$ 0.0001	$ 0.0001		$ 0.0001
Gross Proceeds from issuance of convertible preferred stock, net of issuance costs									$ 113,634,000	$ 4,756,000
Proceeds from initial public offering, net of offering costs									$ 190,710,000	0
Preferred stock, shares issued								0	0		0
Preferred stock issued value								$ 0	$ 0		$ 0
Preferred stock, par value								$ 0.0001	$ 0.0001		$ 0.0001
Accumulated deficit								$ (75,887,000)	$ (75,887,000)		$ (27,098,000)
Payments of Debt Issuance Costs									$ 36,000
Convertible promissory note issued						$ 6,500,000
Sale of common stock							77,418	39,387,389	39,387,389		3,596,936		192,276
Common Stock Shares Outstanding								38,991,403	38,991,403		2,639,026
Restricted common stock, vested									2,261,617		1,995,314
Restricted common stock, Expected to vest								86,012	86,012
Stock option granted vesting period							48 months
Granted									5,982,133
Common Stock, Capital Shares Reserved for Future Issuance								16,004,552	16,004,552
Preferred Stock, Shares Outstanding								0	0		0
Preferred stock, shares authorized		50,000,000						50,000,000	50,000,000		0
Non-cash, stock-based compensation expense									$ 25,354,000	$ 187,000
2021 Stock Incentive Plan
Class Of Stock [Line Items]
Sale of common stock								50,000,000	50,000,000
Stock option granted vesting period									4 years
Stock option granted maximum term									10 years
Percentage of exercise price to fair market value common stock on grant date									100.00%
Common Stock, Capital Shares Reserved for Future Issuance								4,600,000	4,600,000
Tadataka Yamada [Member]
Class Of Stock [Line Items]
Exercise price range, lower range limit	$ 0.83
Exercise price range, upper range limit	$ 5.90
Accelerated vesting of shares	611,639
Non-cash, stock-based compensation expense								$ 21,000,000	$ 21,000,000
Restricted Stock
Class Of Stock [Line Items]
Sale of common stock							2,580,600	2,347,629	2,347,629		269,694
Common Stock Shares Outstanding														968,158
Percentage of Grants Vested							20.00%
Percentage of Issuance Vested							80.00%
Granted								383,500	383,500
Options grant date fair value								$ 9,900,000	$ 9,900,000
Compensation expense recognition vesting period									4 years
Unrecognised compensation cost								$ 9,500,000	$ 9,500,000
Restricted Stock | Management
Class Of Stock [Line Items]
Common stock, par value								$ 0.004	$ 0.004		$ 0.004
Stock Options [Member]
Class Of Stock [Line Items]
Cash received for early exercise of unvested options								$ 200,000	$ 200,000
Weighted-average grant date fair value									$ 8.07
Granted								1,347,511	5,982,133
Options grant date fair value								$ 18,900,000	$ 44,400,000
Compensation expense recognition vesting period									3 years 7 months 17 days
Unrecognised compensation cost								$ 38,300,000	$ 38,300,000
Stock Options [Member] | 2021 Stock Incentive Plan
Class Of Stock [Line Items]
Percentage of exercise price to fair market value common stock on grant date									110.00%
IPO [Member]
Class Of Stock [Line Items]
Proceeds from initial public offering, net of offering costs		$ 190,700,000
Sale of common stock		12,133,333
Conversion of Stock, Shares Converted		21,634,898	21,634,898
Preferred Stock, Shares Outstanding		89,908,215						0	0
2021 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Sale of common stock				15,000,000
Common Stock, Capital Shares Reserved for Future Issuance				400,000
Percentage Of Common Stock Outstanding				1.00%
Number of purchased shares by the employee									0
Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Convertible preferred stock, shares authorized								0	0		54,039,749
Convertible preferred stock, par value								$ 0.0001	$ 0.0001		$ 0.0001
Convertible preferred stock, shares issued								0	0		32,198,879
Preferred stock, par value												$ 0.0001
Series A1 Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock, shares issued					21,944,874
Series B Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, shares issued												35,764,462
Series B1 Convertible Preferred Stock
Class Of Stock [Line Items]
Preferred stock, shares issued												32,958,612
Series B-2 Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, shares issued												2,805,850

Convertible Preferred Stock a_5

Convertible Preferred Stock and Stockholders' Equity (Deficit) - Summary of the Status of the Options Issued Under the Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Stockholders' Equity Note [Abstract]
Option Pool Available for Grant, Balance at December 31, 2020	541,411
Option Pool Available for Grant, Authorized increase in plan shares	22,634,965
Option Pool Available for Grant, Granted	(5,982,133)
Option Pool Available for Grant, Balance at September 30, 2021	17,194,243	541,411
Options Outstanding, Balance at December 31, 2020	641,427
Options Outstanding, Granted	5,982,133
Options Outstanding, Exercised (including early)	(202,223)
Options Outstanding, Balance at September 30, 2021	6,421,337	641,427
Options Outstanding, Vested and expected to vest as of September 30, 2021	6,421,337
Options Outstanding, Vested and exercisable at September 30, 2021	726,036
Weighted average exercise price per share, Balance at December 31, 2020	$ 0.83
Weighted average exercise price per share, Granted	8.07
Weighted average exercise price per share, Exercised (including early)	0.83
Weighted average exercise price per share, Balance at September 30, 2021	7.57	$ 0.83
Weighted average exercise price per share, Vested and expected to vest as of September 30, 2021	7.57
Weighted average exercise price per share, Vested and exercisable at September 30, 2021	$ 5.09
Weighted average remaining contractual term (Years)	9 years 2 months 1 day	9 years 7 days
Weighted average remaining contractual term, Vested and expected to vest as of September 30, 2021	9 years 2 months 1 day
Weighted average remaining contractual term, Vested and exercisable at September 30, 2021	9 years 3 months 14 days
Aggregate intrinsic value, Balance at December 31, 2020	$ 0
Aggregate intrinsic value, Exercised (including early)	1,101,195
Aggregate intrinsic value, Balance at September 30, 2021	154,954,478	$ 0
Vested and expected to vest as of September 30, 2021	154,954,478
Aggregate intrinsic value, Vested and exercisable at September 30, 2021	$ 17,789,497

Convertible Preferred Stock a_6

Convertible Preferred Stock and Stockholders' Equity (Deficit) - Schedule of Common Stock Reserved for Future Issuance (Details)	Sep. 30, 2021shares
Class Of Stock [Line Items]
Convertible preferred stock	16,004,552
Equity Incentive Plan [Member]
Class Of Stock [Line Items]
Convertible preferred stock	8,383,215
2021 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Convertible preferred stock	1,200,000
Common Stock Options and Restricted Stock Units [Member]
Class Of Stock [Line Items]
Convertible preferred stock	6,421,337

Convertible Preferred Stock a_7

Convertible Preferred Stock and Stockholders' Equity (Deficit) - Schedule of Stock-based Compensation Expense for All Equity Awards (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Class Of Stock [Line Items]
Research and development	$ 23,670	$ 70	$ 25,354	$ 187
Research and Development Expense [Member]
Class Of Stock [Line Items]
Research and development	931	32	1,471	87
General and Administrative [Member]
Class Of Stock [Line Items]
Research and development	$ 22,739	$ 38	$ 23,883	$ 100

Convertible Preferred Stock a_8

Convertible Preferred Stock and Stockholders' Equity (Deficit) - Summary of Assumptions Used in Black-Scholes Model (Details)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Class Of Stock [Line Items]
Risk-free rate of interest, Minimum	0.53%	0.31%
Risk-free rate of interest, Mximum	1.23%	1.40%
Expected stock price volatility, Minimum	86.00%	80.20%
Expected stock price volatility, Maximum	88.40%	86.40%
Dividend yield	0.00%	0.00%
Minimum [Member]
Class Of Stock [Line Items]
Expected term (years)	5 years 1 month 2 days	5 years 10 months 24 days
Maximum [Member]
Class Of Stock [Line Items]
Expected term (years)	6 years 5 months 26 days	6 years 29 days

Income Taxes (Additional Inform

Income Taxes (Additional Information) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Effective Income Tax Rate	0.00%	0.00%	0.00%	0.00%
Difference Between Effective Tax Rate			0.00%
Federal Statutory Rate	21.00%	21.00%	21.00%	21.00%

Employee Savings Plan - Additio

Employee Savings Plan - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Defined Contribution Plan Disclosure [Line Items]
Employer discretionary contribution amount	$ 0		$ 0
Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Percent of employees gross pay		90.00%