Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2022	May 09, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Mar. 31, 2022
Document Fiscal Year Focus	2022
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q1
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		39,726,829