SCHEDULE 13D/A 0001193125-22-143660 0001863769 XXXXXXXX LIVE 5 Common Stock, par value $0.0001 per share 09/17/2025 false 0001888012 43157M102 HILLEVAX, INC.

321 Harrison Avenue Boston MA 02118

Steve R. Bailey (206) 621-7200 601 Union Street, Suite 3200 Seattle WA 98101 0001863769 N Frazier Life Sciences Public Fund, L.P. b WC N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 PN 0001879466 N FHMLSP, L.P. b AF N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 PN 0001879465 N FHMLSP, L.L.C. b AF N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 OO 0001913804 N Frazier Life Sciences Public Overage Fund, L.P. b WC N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 PN 0001963247 N FHMLSP Overage, L.P. b AF N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 PN 0001963248 N FHMLSP Overage, L.L.C. b AF N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 OO 0001790879 N Frazier Life Sciences X, L.P. b WC N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 PN 0001790880 N FHMLS X, L.P. b AF N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 PN 0001790811 N FHMLS X, L.L.C. b AF N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 OO 0001911592 N Frazier Life Sciences XI, L.P. b WC N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 PN 0001911580 N FHMLS XI, L.P. b AF N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 PN 0001911623 N FHMLS XI, L.L.C. b AF N DE 0.00 0.00 0.00 0.00 0.00 N 0.0 OO 0001341382 N James N. Topper b AF N X1 0.00 0.00 0.00 0.00 0.00 N 0.0 IN 0001365617 N Patrick J. Heron b AF N X1 0.00 0.00 0.00 0.00 0.00 N 0.0 IN 0001397906 N Albert Cha b AF N X1 0.00 0.00 0.00 0.00 0.00 N 0.0 IN 0001865123 N James Brush b AF N X1 0.00 0.00 0.00 0.00 0.00 N 0.0 IN 0001702527 N Daniel Estes b AF N X1 0.00 0.00 0.00 0.00 0.00 N 0.0 IN Common Stock, par value $0.0001 per share HILLEVAX, INC. 321 Harrison Avenue Boston MA 02118 This Amendment No. 5 ("Amendment No. 5") to Schedule 13D amends the statement on Schedule 13D filed on May 6, 2022 (the "Original Schedule 13D") as amended on September 8, 2022, May 5, 2023, September 27, 2023 and May 31, 2024 (the "Prior Amendments", and together with the Original Schedule 13D and this Amendment No. 5, the "Schedule 13D"). Except as otherwise specified in Amendment No. 5, all items in the Original Schedule 13D, as amended by the Prior Amendments, are unchanged. All capitalized terms used in this Amendment No. 5 and not otherwise defined herein have the meanings ascribed to such terms in the Original Schedule 13D, as amended by the Prior Amendments. Item 4 of the Schedule 13D is hereby amended to incorporate the following at the end thereof: On August 4, 2025, the Issuer, XOMA Royalty Corporation ("Purchaser") and XRA 4 Corp., a wholly owned subsidiary of Purchaser ("Merger Sub") entered into an Agreement and Plan of Merger (the "Merger Agreement"). Pursuant to the Merger Agreement, upon the terms and subject to the conditions thereof, Purchaser commenced a tender offer (the "Offer") to acquire all of the outstanding shares of Common Stock of the Issuer (the "Shares"), at an offer price of (i) $1.95 in cash, without interest, plus (ii) one non-transferable contractual contingent value right per Share (collectively, the "Offer Price"). The Offer expired at the end of the day, one minute after 11:59 p.m. Eastern Time, on September 15, 2025. On September 17, 2025, Purchaser accepted for purchase all shares of Common Stock that were validly tendered and not validly withdrawn in accordance with the terms of the Offer, which included the Shares that were held by the Reporting Persons. On September 17, 2025, upon the terms and subject to the conditions set forth in the Merger Agreement and in accordance with Section 251(h) of the Delaware General Corporation Law, Merger Sub merged with and into the Issuer, with the Issuer surviving as a wholly owned subsidiary of Purchaser (the "Merger"), without a meeting or vote of stockholders of the Issuer (the "Effective Time"). At the Effective Time, the Shares held by the Reporting Persons were each converted into the right to receive the Offer Price. In addition, pursuant to the Merger Agreement, at the Effective Time, each outstanding stock option, whether vested or unvested, that had an exercise price per Share that was greater than the Offer Price was canceled for no consideration. This included the stock options held by Heron. The information contained in Rows 7, 8, 9, 10, 11, and 13 of each Reporting Person's cover page to this Schedule 13D is incorporated by reference into this Item 5. Except as specifically stated herein, the filing of this Schedule 13D shall not be construed as an admission that any Reporting Person or any of the foregoing is, for the purposes of Section 13(d) and/or Section 13(g) of the Act or otherwise, the beneficial owner of any securities covered by this Schedule 13D or a member of a "group" with any other person. The information contained in Rows 7, 8, 9, 10, 11, and 13 of each Reporting Person's cover page to this Schedule 13D is incorporated by reference into this Item 5. Except as disclosed in Item 4 of this Schedule 13D, none of the Reporting Persons has effected any transactions relating to the Common Stock during the past 60 days. As of September 17, 2025, the Reporting Persons ceased to be beneficial owners of more than five percent of the Shares. Exhibit 99.1 Joint Filing Agreement (incorporated by reference to Exhibit A to Schedule 13D/A filed on May 31, 2024) Frazier Life Sciences Public Fund, L.P. /s/ Steve R. Bailey 09/17/2025 FHMLSP, L.P. /s/ Steve R. Bailey 09/17/2025 FHMLSP, L.L.C. /s/ Steve R. Bailey 09/17/2025 Frazier Life Sciences Public Overage Fund, L.P. /s/ Steve R. Bailey 09/17/2025 FHMLSP Overage, L.P. /s/ Steve R. Bailey 09/17/2025 FHMLSP Overage, L.L.C. /s/ Steve R. Bailey 09/17/2025 Frazier Life Sciences X, L.P. /s/ Steve R. Bailey 09/17/2025 FHMLS X, L.P. /s/ Steve R. Bailey 09/17/2025 FHMLS X, L.L.C. /s/ Steve R. Bailey 09/17/2025 Frazier Life Sciences XI, L.P. /s/ Steve R. Bailey 09/17/2025 FHMLS XI, L.P. /s/ Steve R. Bailey 09/17/2025 FHMLS XI, L.L.C. /s/ Steve R. Bailey 09/17/2025 James N. Topper /s/ Steve R. Bailey 09/17/2025 Patrick J. Heron /s/ Steve R. Bailey 09/17/2025 Albert Cha /s/ Steve R. Bailey 09/17/2025 James Brush /s/ Steve R. Bailey 09/17/2025 Daniel Estes /s/ Steve R. Bailey 09/17/2025