X0508 4 2023-12-20 0 0001786255 Icosavax, Inc. ICVX 0001873839 Simpson Adam K. C/O ICOSAVAX, INC. 1930 BOREN AVE., SUITE 1000 SEATTLE WA 98101 1 1 0 0 Chief Executive Officer 1 Common Stock 2023-12-20 4 S 0 62205 15.4571 D 184724 D Common Stock 2023-12-21 4 M 0 102574 1.04 A 287298 D Common Stock 2023-12-21 4 M 0 40000 2.47 A 327298 D Common Stock 2023-12-21 4 M 0 23343 0.84 A 350641 D Common Stock 2023-12-21 4 S 0 50000 15.4444 D 300641 D Common Stock 2023-12-21 4 S 0 40000 15.4265 D 260641 D Common Stock 531576 I By family trust Common Stock 129032 I By family trust Common Stock 129032 I By family trust Stock Option (Right to Buy) 1.04 2023-12-21 4 M 0 102574 0.00 D 2031-01-28 Common Stock 102574 314676 D Stock Option (Right to Buy) 2.47 2023-12-21 4 M 0 40000 0.00 D 2032-11-09 Common Stock 40000 237146 D Stock Option (Right to Buy) 0.84 2023-12-21 4 M 0 23343 0.00 D 2030-05-10 Common Stock 23343 4789 D Reflects shares sold to cover withholding taxes upon accelerated vesting of restricted stock unit awards pursuant to a Rule10b5-1 instruction letter dated December 6, 2021. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $15.41 to $15.50. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The sales were effected pursuant to a Rule 10b5-1 instruction letter dated December 6, 2021. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $15.39 to $15.60. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $15.40 to $15.495. The Reporting Person undertakes to provide the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. 25% of the shares subject to the option vested on January 14, 2022, and 1/48th of the shares subject to the option vest monthly thereafter. One-third (1/3rd) of the shares subject to the option shall vest on each of the first three anniversaries of November 10, 2022, subject to the reporting person's continued service through the applicable vesting date. 25% of the shares subject to the option vested on February 21, 2021, and 1/48th of the shares subject to the option vest monthly thereafter. /s/ Elizabeth Bekiroglu, Attorney-in-Fact 2023-12-22