Sec Form 4 Filing - RA CAPITAL MANAGEMENT, L.P. @ Icosavax, Inc. - 2024-02-19

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person RA CAPITAL MANAGEMENT, L.P. 2. Issuer Name and Ticker or Trading Symbol Icosavax, Inc. [ ICVX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 200 BERKELEY STREET, 18TH FLOOR, 3. Date of Earliest Transaction (MM/DD/YY) 02/19/2024 (Street) BOSTON, MA02116 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 02/19/2024 U 5,543 D 0 I See footnote ( 2 ) ( 3 ) Common Stock 02/19/2024 U 5,324,897 D 0 I See footnote ( 2 ) ( 4 ) Common Stock 02/19/2024 U 638,668 D 0 I See footnote ( 2 ) ( 5 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Stock Option (Right to Buy) $ 6.25 02/19/2024 D 22,278 ( 6 ) ( 6 ) Common Stock 22,278 ( 6 ) 0 I See footnote ( 2 ) ( 3 ) Stock Option (Right to Buy) $ 9.89 02/19/2024 D 17,000 ( 6 ) ( 6 ) Common Stock 17,000 ( 6 ) 0 I See footnote ( 2 ) ( 3 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X X RA Capital Healthcare Fund LP 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X X RA Capital Nexus Fund II, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X X Kolchinsky Peter C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X X Shah Rajeev M. C/O RA CAPITAL MANAGEMENT, L.P. 200 BERKELEY STREET, 18TH FLOOR BOSTON, MA02116 X X Signatures /s/ Peter Kolchinsky, Manager of RA Capital Management, L.P. 02/20/2024 Signature of Reporting Person Date /s/ Peter Kolchinsky, Manager of RA Capital Healthcare Fund GP, LLC the General Partner of RA Capital Healthcare Fund, L.P. 02/20/2024 Signature of Reporting Person Date /s/ Peter Kolchinsky, Manager of RA Capital Nexus Fund II GP, LLC the General Partner of RA Capital Nexus Fund II, L.P. 02/20/2024 Signature of Reporting Person Date /s/ Peter Kolchinsky, individually 02/20/2024 Signature of Reporting Person Date /s/ Rajeev Shah, individually 02/20/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )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. ( 2 )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. ( 3 )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. ( 4 )Held by the Fund. ( 5 )Held by the Nexus Fund II. ( 6 )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.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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