Study findings demonstrate that a booster dose of inactivated COVID-19 vaccine produces a highly sifted, humoral immune response via a sustained evolution of antibodies, able to effectively neutralize SARS-CoV-2 variants of concern.

SINOVAC Biotech Ltd. (NASDAQ: SVA) (“Sinovac” or the “Company”), a leading provider of biopharmaceutical products in China, announced a paper, titled “A third dose of inactivated vaccine augments the potency, breadth, and duration of anamnestic responses against SARS-CoV-2,” is available on medRxiv. The findings suggest a third dose of CoronaVac® can induce a better neutralization breadth to variants of concern (“VOCs”), including the Delta variant, a rapid immunological memory response, and a long-lasting humoral response. Having a third dose of inactivated COVID-19 vaccine is more effective for COVID-19 prevention.

This study includes an in-depth exploration of the immunogenic profiles of antibodies from three and two-dose CoronaVac® recipients and convalescents. The findings indicate that three-dose vaccinees demonstrated better neutralization breadth to VOCs, expeditious recall, and long-lasting humoral immune response. Analysis of 171 complex structures of neutralizing antibodies identified structure-activity correlation and revealed ultrapotent, VOCs-resistant, and broad-spectrum patches.

As part of this study, researchers also constructed immunogenic and mutational heat maps, which revealed a direct relationship between “hot” immunogenic sites and areas with high mutation frequencies. Prolonged and repeated antigen stimulation can induce ongoing antibody somatic mutation, memory B cell clonal turnover, and antigen composition changes in B cell repertoire, which result in the development of monoclonal antibodies with enhanced neutralizing potency and breadth.

The above research provides a theoretical basis for a third dose of inactivated COVID-19 vaccine.

About SINOVAC

SINOVAC Biotech Ltd. is a China-based biopharmaceutical company that focuses on the research, development, manufacturing and commercialization of vaccines that protect against human infectious diseases. SINOVAC's product portfolio includes vaccines against COVID-19, enterovirus71 (EV71), hepatitis A and B, seasonal influenza, 23-Valent pneumococcal polysaccharide (“PPV”), H5N1 pandemic influenza (avian flu), H1N1 influenza (swine flu), varicella, mumps and Poliomyelitis. SINOVAC’s COVID-19 vaccine, CoronaVac®, has been granted emergency use approval or conditional marketing authorization by over 50 countries or regions worldwide. Healive®, the hepatitis A vaccine manufactured by the Company, has passed the assessment under WHO prequalification procedures in 2017. The EV71 vaccine, an innovative vaccine developed by SINOVAC against hand foot and mouth disease caused by EV71, was commercialized in China in 2016. In 2009, SINOVAC was the first company worldwide to receive approval for its H1N1 influenza vaccine, which it has supplied to the Chinese Government's vaccination campaign and stockpiling program. The Company is also the only supplier of the H5N1 pandemic influenza vaccine to the government stockpiling program. In 2021, SINOVAC’s Sabin-strain inactivated polio vaccine has approved for registration. The Company is developing several new products including combined vaccines. SINOVAC primarily sells its vaccines in China, while also exploring growth opportunities in international markets. The Company is seeking market authorization of its products in over 30 countries outside of China. For more information, please see the Company’s website at www.sinovac.com.

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