| Cover | Feb. 19, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 19, 2024 |
| Current Fiscal Year End Date | --12-31 |
| Entity File Number | 001-40655 |
| Entity Registrant Name | ICOSAVAX, INC. |
| Entity Central Index Key | 0001786255 |
| Entity Tax Identification Number | 82-3640549 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 1930 Boren Avenue |
| Entity Address, Address Line Two | Suite 1000 |
| Entity Address, City or Town | Seattle |
| Entity Address, State or Province | WA |
| Entity Address, Postal Zip Code | 98101 |
| City Area Code | 206 |
| Local Phone Number | 737-0085 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.0001 per share |
| Trading Symbol | ICVX |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
