SAIF Partners Files Definitive Proxy Materials in Connection with Sinovac Biotech 2025 Special Meeting of Shareholders; Nominates Ten Highly Qualified Director Candidates to the Board

Sends Open Letter to Sinovac Shareholders Calling for a New Board to End Years of Chaos at Sinovac

SAIF Nominees Will Work to Resolve Costly Legal Battles, Take Action to Resume Stock Trading after Six-Year Halt, and Facilitate Distribution of Cash That Rightfully Belongs to Shareholders

Urges Sinovac Shareholders to VOTE the GOLD Proxy Card FOR the Election of SAIF's Director Nominees

SAIF Partners IV L.P., ("SAIF Partners"), the largest single investor in Sinovac Biotech Ltd. ("Sinovac" or the "Company"), beneficially owning approximately 15% of the outstanding common shares, today announced that it has filed a definitive proxy statement for the election of ten director nominees to Sinovac's Board of Directors (the "Board") in connection with the special meeting of the shareholders of the Company 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), and at any adjourned, postponed, continued, or rescheduled meeting thereof (the "Special Meeting").

Additionally, SAIF Partners issued an open letter to its fellow Sinovac shareholders outlining its belief that new highly qualified directors are required to effectively resolve the significant challenges Sinovac currently faces and deliver value for all shareholders. In the letter, SAIF details how the Board has not effectively guided Sinovac after the significant chaos of the past several years, including, among other issues, strategic missteps, costly and distracting legal battles, a stock that does not trade, and a large amount of cash that the Company is inexplicably retaining rather than distributing it to shareholders as they should.

If elected, SAIF Partners' nominees will work with management to develop a plan to address these issues and bring disciplined corporate governance, proper capital allocation, strategic foresight and operational excellence to Sinovac. SAIF Partners has outlined the most critical priorities for Sinovac that their nominees would seek to address if elected, including declaring additional dividends, resuming trading of common shares and resolving shareholder disputes.

The full text of the letter is below.

June 16, 2025

Dear Fellow Sinovac Shareholder:

As the largest single investor and a long-term shareholder in Sinovac Biotech Ltd. ("Sinovac" or the "Company"), beneficially owning approximately 15% of the outstanding common shares, SAIF Partners ("SAIF") believes deeply in the Company's products and tremendous potential to create long-lasting value for all shareholders. However, Sinovac's Board of Directors (the "Board") has not effectively guided Sinovac after the significant chaos of the past several years, including, among other issues, strategic missteps, costly and distracting legal battles, a stock that does not trade, and a large amount of cash that the Company is inexplicably retaining rather than distributing it to shareholders as they should.

The Board has done nothing to address these issues and only began to acknowledge them after we forced Sinovac to hold a special meeting to replace directors. Simply put, the status quo is not working.

Sinovac desperately needs new and experienced directors dedicated to putting Sinovac back on the right track through disciplined corporate governance, proper capital allocation, strategic foresight and operational excellence – and acting in the best interests of ALL Sinovac shareholders. As such, SAIF is nominating highly qualified candidates for election to the Board at the special meeting of shareholders to be held July 8, 2025.

We have taken this important action to address key issues at Sinovac that, if elected, will be top priorities for our nominees, including:

1. Declaration of Additional Dividend. We believe there are billions of US dollars of available cash in Sinovac's accounts and that Sinovac can and should pay more dividends to shareholders in addition to the $55.00 per share special dividend declared by the Board on April 1, 2025, which would not have been announced without our engagement. Further, dividends have been paid from Sinovac subsidiaries, but not to shareholders.

Our nominees will determine, in close collaboration with management, on the appropriate allocation of retained earnings and facilitate the distribution of long-overdue returns to all shareholders.

2. Resumption of Trading of Common Shares of the Company. Sinovac shares have not traded for more than six years, denying shareholders the liquidity they deserve.

Our nominees will take immediate steps to address compliance issues and work expeditiously towards the resumption of trading of the Company's shares.

3. Resolution of Shareholder Disputes and Unlocking the Company's Full Potential. Sinovac has been entrapped in endless disputes and prolonged lawsuits since 2018. We are concerned that the series of legal disputes started recently will cause more crisis and destruction to the interests of the Company and its shareholders.

Our nominees will engage with these shareholders to amicably resolve ongoing disputes, eliminate divisions, and foster alignment among shareholders in order to focus on Sinovac's core mission, and drive growth and value.

4. Strategic Realignment for Shareholder Value Creation. Sinovac's Board does not currently have a strategic plan in place that reflects the realities of the current market environment and positions the Company to capitalize on emerging opportunities in the biopharmaceutical sector.

Our nominees will work closely with Sinovac management to develop a business strategy with clear operational objectives to drive long-term value for all shareholders.

A NEW BOARD IS DESPERATELY NEEDED TO RESTORE CREDIBILITY AND ENSURE SHAREHOLDER VALUE IS NOT FURTHER ERODED

Sinovac shareholders deserve a Board that is unbiased in its decision making and dedicated to acting on behalf of all shareholders rather than for a select few. Presently, all but one member of the Board are representatives of 1Globe and OrbiMed, whose influence far exceeds their respective 9.5% and 3.8% ownership stakes in Sinovac.

We believe our nominees – who represent a broad base of major Sinovac shareholders including Weidong Yin (the CEO and founder of the Company), SAIF Partners, Vivo Capital, CDH Investment, Advantech Capital, and 1Globe – will comprise a well-balanced and diversified Board with extensive industry knowledge, experience and insights necessary to end costly and distracting internal strife, and execute a clear strategic plan that maximizes sustainable, long-term value for ALL shareholders. Certain of our nominees have key management experience at Sinovac and will work closely with the Company management team to drive long-term value for all shareholders.

We urge you to join us and vote the GOLD proxy card in support of our highly qualified nominees who will make the changes necessary to help Sinovac realize its tremendous potential and build the value of Sinovac for all shareholders.

Please vote on the GOLD proxy card TODAY!

Sincerely,

SAIF Partners

About SAIF Partners

SAIF Partners is a leading Asian private equity firm with cumulative assets under management of over $4 billion. SAIF Partners is an active lead investor working closely with its portfolio companies to develop their business both organically and through acquisitions, seeking synergistic cooperation among them, as well as enhancing shareholder value via promotion of good corporate governance and best management practices.

Additional Information and Where to Find It

This communication may be deemed to be solicitation material in respect of SAIF Partners' nomination of ten director nominees to Sinovac's Board. In connection with such solicitation, SAIF Partners mailed the definitive proxy statement and proxy card to shareholders of Sinovac with respect to the Special Meeting to be held in connection with the election of directors to Sinovac's Board. The definitive proxy statement mailed by SAIF Partners is also filed as Exhibit 1 to its Schedule 13D/A filed on or about June 16, 2025. SHAREHOLDERS ARE URGED TO READ THE PROXY STATEMENT (INCLUDING ANY AMENDMENTS OR SUPPLEMENTS THERETO) AND ANY OTHER RELEVANT DOCUMENTS THAT THE COMPANY WILL MAIL AND FILE WITH THE SEC IN CONNECTION WITH THE SINOVAC SPECIAL MEETING, INCLUDING ANY DOCUMENT INCORPORATED BY REFERENCE THEREIN, CAREFULLY IF AND WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION ABOUT THE DIRECTOR NOMINEES AND THE SPECIAL MEETING AND RELATED MATTERS. Sinovac's shareholders may obtain, free of charge, the definitive version of the proxy statement, any amendments or supplements thereto, and any other relevant documents mailed by SAIF Partners in connection with the Special Meeting at proxyvoting.com/SVA/documents.

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