Exhibit (a)(1)(C)​

Offer To Purchase
All Outstanding Shares of Common Stock
of

ICOSAVAX, INC.

at
$15.00 per share in cash, plus one non-transferable contingent value right per share representing the right to receive a contingent payment of up to $5.00 in cash on the achievement of specified milestones
by

ISOCHRONE MERGER SUB INC.

a wholly owned subsidiary of

ASTRAZENECA FINANCE AND HOLDINGS INC.

a wholly owned subsidiary of

ASTRAZENECA PLC

THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT ONE MINUTE AFTER 11:59 P.M., NEW YORK CITY TIME, ON JANUARY 26, 2024, UNLESS THE OFFER IS EXTENDED
OR EARLIER TERMINATED.

December 27, 2023​

To Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees:

We have been engaged by Isochrone Merger Sub Inc., a Delaware corporation (“Merger Sub”) and wholly owned subsidiary of AstraZeneca Finance and Holdings Inc., a Delaware corporation (“Parent”), to act as information agent (the “Information Agent”) in connection with Merger Sub’s offer to purchase all of the outstanding shares of common stock, par value $0.0001 per share (the “Shares”), of Icosavax, Inc., a Delaware corporation (the “Company”), in exchange for (i) $15.00 per Share in cash, subject to applicable withholding taxes and without interest (the “Closing Amount”), plus (ii) one non-transferable contingent value right (each, a “CVR”) per Share representing the right to receive a contingent payment of up to $5.00 in cash, subject to applicable withholding taxes and without interest, on achievement of specified milestones on or prior to the applicable outside date on the terms and subject to the other conditions set forth in the Contingent Value Rights Agreement (the Closing Amount plus one CVR, collectively, or any greater amount per Share that may be paid pursuant to the Offer (as defined below), the “Offer Price”), on the terms and subject to the conditions set forth in the Offer to Purchase (as it may be amended, supplemented or otherwise modified from time to time, the “Offer to Purchase”) and in the related Letter of Transmittal (as it may be amended, supplemented or otherwise modified from time to time, the “Letter of Transmittal,” which, together with the Offer to Purchase, as they may be amended, supplemented or otherwise modified from time to time, collectively constitute the “Offer”).

The conditions to the Offer are described in Section 15 of the Offer to Purchase.

For your information and for forwarding to your clients for whom you hold Shares registered in your name or in the name of your nominee, we are enclosing the following documents:

1.

The Offer to Purchase;

2.

The Letter of Transmittal (including Guidelines for Certification of Taxpayer Identification Number on IRS Form W-9) for your use in accepting the Offer and tendering Shares and for the information of your clients;

3.

A form of letter which may be sent to your clients for whose accounts you hold Shares registered in your name or in the name of your nominee, with space provided for obtaining such clients’ instructions with regard to the Offer;

4.

The Company’s Solicitation/Recommendation Statement on Schedule 14D-9; and

5.

For your use only, a return envelope addressed to Equiniti Trust Company, LLC, which is the depositary for the Offer (the “Depositary”).

We urge you to contact your clients as promptly as possible. Please note that the Offer and withdrawal rights will expire one minute after 11:59 p.m., New York City time, on January 26, 2024, unless the Offer is extended or earlier terminated. We are not providing for guaranteed delivery procedures.

The Offer is being made pursuant to an Agreement and Plan of Merger, dated as of December 11, 2023 (as it may be amended, supplemented or otherwise modified from time to time, the “Merger Agreement”), by and among the Company, Parent and Merger Sub, pursuant to which, as soon as practicable following the consummation of the Offer, and in any event no later than one business day thereafter, subject to the satisfaction or waiver of certain conditions, Merger Sub will merge with and into the Company (the “Merger”), and the Company will survive the Merger (the “Surviving Corporation”) as a wholly owned subsidiary of Parent, on the terms and subject to the conditions set forth in the Merger Agreement. If Merger Sub consummates the Offer, the Merger Agreement contemplates that the parties will as promptly as practicable thereafter effect the closing of the Merger without a vote of the stockholders of the Company in accordance with Section 251(h) of the DGCL, subject to the satisfaction or waiver of certain conditions.

At the effective time of the Merger (being the time and day of the filing of the certificate of merger with the Secretary of State of the State of Delaware or at such later time and day as may be agreed in writing by Parent and the Company and specified in the certificate of merger in accordance with the DGCL, the “Effective Time”), each Share issued and outstanding immediately prior to the Effective Time (excluding Shares owned by Parent, Merger Sub or the Company, or by any direct or indirect wholly owned subsidiary of Parent or Merger Sub, any Shares irrevocably accepted for payment pursuant to the Offer, and any Shares held by stockholders who are entitled to demand, and who shall have properly and validly demanded their statutory rights of appraisal in respect of such Shares in compliance with Section 262 of the DGCL) shall be canceled and extinguished and automatically converted into the right to receive the Offer Price (including the CVR), without interest thereon and subject to any applicable withholding tax. As a result of the Merger, the Company will cease to be a publicly traded company and will become a wholly owned subsidiary of Parent.

The board of directors of the Company has unanimously: (i) determined that the Merger Agreement and the transactions contemplated thereby, including the Offer and the Merger, are advisable, fair to and in the best interests of the Company and its stockholders, and declared it advisable for the Company to enter into the Merger Agreement, (ii) approved and declared advisable the execution and delivery by the Company of the Merger Agreement, the performance by the Company of its covenants and agreements contained therein and the consummation of the Offer and the Merger and the other transactions contemplated by the Merger Agreement on the terms and subject to the conditions contained therein and (iii) resolved, subject to the terms and conditions set forth in the Merger Agreement, to recommend that the holders of the Shares accept the Offer and tender their Shares to Merger Sub pursuant to the Offer.

For Shares to be validly tendered to Merger Sub and accepted for payment pursuant to the Offer (i) the certificates evidencing such Shares (the “Share Certificates”) or confirmation of a book-entry transfer of such Shares into the Depositary’s account at The Depository Trust Company pursuant to the procedures set forth in Section 3 of the Offer to Purchase, (ii) in the case of Share Certificates, the Letter of Transmittal, properly completed and duly executed, with any required signature guarantees and (iii) any other documents required by the Letter of Transmittal or, in the case of a book-entry transfer, an “agent’s message” in lieu of the Letter of Transmittal and such other documents, must be timely received by the Depositary.

Merger Sub will not pay any fees or commissions to any broker or dealer or to any other person (other than to the Depositary and the Information Agent as described in Section 18 of the Offer to Purchase) in connection with the solicitation of tenders of Shares pursuant to the Offer. Brokers, dealers, commercial

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banks and trust companies will, on request, be reimbursed by Merger Sub for customary mailing and handling expenses incurred by them in forwarding offering materials to their customers. Merger Sub will pay all stock transfer taxes applicable to its purchase of Shares pursuant to the Offer, subject to Instruction 6 of the Letter of Transmittal.

Any inquiries you may have with respect to the Offer should be addressed to, and additional copies of the enclosed materials may be obtained from, the undersigned at the address and telephone numbers set forth below and on the back cover of the Offer to Purchase.

Very truly yours,

Innisfree M&A Incorporated

Nothing contained herein or in the enclosed documents shall render you, any agent of Merger Sub, the Information Agent or the Depositary or any affiliate of any of them or authorize you or any other person to use any document or make any statement on behalf of any of them in connection with the Offer other than the enclosed documents and the statements contained therein.

The Information Agent for the Offer is:

Innisfree M&A Incorporated
501 Madison Avenue, 20th floor
New York, New York 10022
Stockholders may call toll free: (888) 750-5835
Banks and Brokers may call collect: (212) 750-5833

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