RA CAPITAL MANAGEMENT, L.P. - 19 Feb 2024 Form 4 Insider Report for Icosavax, Inc.

Footnote F1

In connection with the terms of an Agreement and Plan of Merger, dated as of December 11, 2023 (the "Merger Agreement"), by and among the Issuer, AstraZeneca Finance and Holdings Inc. ("Parent"), and Isochrone Merger Sub Inc., a wholly owned subsidiary of Parent ("Purchaser"), Purchaser completed a tender offer for shares of the Issuer's Common Stock at a purchase price per share of (i) $15.00 plus (ii) one non-tradable contingent value right ("CVR") per share representing the right to receive a contingent payment of up to $5.00 in cash upon achievement of specified milestones (collectively, the "Offer Price"). After completion of the tender offer, Purchaser merged with and into the Issuer (the "Merger"), effective as of February 19, 2024 (the "Effective Time"), with the Issuer continuing as the surviving entity and a wholly owned subsidiary of Parent.

Footnote F2

RA Capital Management, L.P. (the "Adviser") is the investment manager for RA Capital Healthcare Fund, L.P. (the "Fund") and RA Capital Nexus Fund II, L.P. (the "Nexus Fund II"). The general partner of the Adviser is RA Capital Management GP, LLC (the "Adviser GP"), of which Dr. Peter Kolchinsky and Mr. Rajeev Shah are the managing members. The Adviser, the Adviser GP, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of any of the reported securities, except to the extent of their pecuniary interest therein.

Footnote F3

Under Dr. Kolchinsky's arrangement with the Adviser, Dr. Kolchinsky held these options and shares for the benefit of the Fund and the Nexus Fund II. Dr. Kolchinsky is obligated to turn over to the Adviser any net cash received upon the disposition of the options and shares, which will offset advisory fees owed by the Fund and the Nexus Fund II to the Adviser. The Reporting Persons therefore disclaim beneficial ownership of these options and shares except to the extent of their pecuniary interest.

Footnote F4

Held by the Fund.

Footnote F5

Held by the Nexus Fund II.

Footnote F6

Pursuant to the terms of the Merger Agreement, immediately prior to the Effective Time, this stock option was cancelled and converted into the right to receive, subject to the terms of the Merger Agreement, (a) an amount in cash equal to the product obtained by multiplying (1) the aggregate number of shares underlying such stock option immediately prior to the Effective Time by (2) an amount equal to (A) $15.00 less (B) the exercise price of such stock option, plus (b) one CVR for each share underlying such stock option immediately prior to the Effective Time.