SCHEDULE 13D/A 0001127855-08-000026 0001264738 XXXXXXXX LIVE 5 Common Shares 06/16/2025 false 0001084201 P8696W104 SINOVAC BIOTECH LTD.

No. 39 Shangdi Xi Rd Haidian District Beijing F4 100085

Weidong Yin 86-10-8289-0088 No. 39 Shangdi Xi Road Haidian District Beijing F4 100085 0001264738 N Weidong Yin b PF N F4 6359500.00 0.00 6359500.00 0.00 6359500.00 N 8.85 IN Comments to item 13: Calculation is based on 71,860,702 Common Shares of the Issuer outstanding as of March 31, 2024 according to the Issuer's annual report on Form 20-F for the fiscal year ended December 31, 2023 (the "2023 Annual Report"). Common Shares SINOVAC BIOTECH LTD. No. 39 Shangdi Xi Rd Haidian District Beijing F4 100085 This Amendment No.5 to Schedule 13D is being filed on behalf of Weidong Yin (the "Reporting Person"), to amend the Schedule 13D relating to the common shares, par value $0.001 per share (the "Common Shares"), of Sinovac Biotech Ltd. (the "Issuer"), filed by the Reporting Person on February 7, 2008, as amended by Amendment No.1 to Schedule 13D filed on February 8, 2016, Amendment No.2 to Schedule 13D filed on June 27, 2017, Amendment No.3 to Schedule 13D filed on March 21, 2025, and Amendment No.4 to Schedule 13D filed on April 30, 2025 (collectively, the "Original Schedule 13D"). The information in each Item below amends the information disclosed under the corresponding Item of the Original Schedule 13D. Except as amended and supplemented herein, the information set forth in the Original Schedule 13D remains unchanged. Capitalized terms used herein have meanings as assigned thereto in the Original Schedule 13D unless defined herein. The information set forth in response to each separate Item below shall be deemed to be a response to all Items where such information is relevant. Item 4 is hereby amended and supplemented to add the following: On June 17, 2025, SAIF Partners IV L.P. ("SAIF") filed an amendment to its Schedule 13D, announcing that it has mailed its definitive proxy materials to shareholders of the Issuer, in connection with the special meeting of shareholders of the Issuer to be held on Tuesday, July 8, 2025 at 8 p.m. Atlantic Standard Time (Wednesday, July 9, 2025 at 8:00 a.m. China Standard Time) for the purposes of, among other things, nominating a few persons, including the Reporting Person, to the board of directors of the Company (the "Board"). Before the definitive proxy materials were mailed, SAIF discussed with the Reporting Person the proposal to nominate the Reporting Person to the Board. The Reporting Person and SAIF have not reached any agreement on cooperation or voting. Except as set forth in this statement, the Reporting Person has no present plan or intention which would result in or relate to any of the transactions described in clauses (a) through (j) of Item 4 of Schedule 13D. The Reporting Person anticipates that further communications may occur with SAIF and other shareholders regarding the proxy materials and the special meeting. Depending upon, among other things, the outcome of these communications, the financial condition, results of operations and prospects of the Issuer, conditions in the securities markets, general economic conditions and other factors that the Reporting Person deem relevant, the Reporting Person may take steps and pursue other plans or proposals that relate to or would result in any of the matters set forth in clauses (a) through (j) of Item 4 of Schedule 13D. Item 6 is hereby amended and supplemented to add the following: Item 4 of Amendment No. 5 is incorporated herein by reference. Weidong Yin /s/ Weidong Yin 06/19/2025