SINOVAC Announces Positive Data on Booster Dose of CoronaVac®

CoronaVac® generates good immune memory after the second dose

Third dose of CoronaVac® induces strong immune response

No serious adverse reactions reported

Adverse reactions reported within 28 day after the third dose were even less than those reported within 28 days after the second dose

BEIJING, China, July 27, 2021 -- SINOVAC Biotech Ltd. (NASDAQ: SVA) (“Sinovac” or the “Company”), a leading provider of biopharmaceutical products in China, announced today the pre-print of a paper, titled Immunogenicity and safety of a third dose, and immune persistence of CoronaVac vaccine in healthy adults aged 18-59 years: interim results from a double-blind, randomized, placebo-controlled phase 2 clinical trial, available on Medrxiv. The paper includes published data on immunogenicity and safety profiles of homologous two-dose schedules, as well as interim results on immune persistence, and the immunogenicity and safety of a third dose of CoronaVac®.


The results indicate that a two-dose schedule generates good immune memory. After a third dose was given 6-8 months after the second dose, strong immune response was induced quickly and the neutralizing antibody titers at day 28 after the third dose increased by three to five times higher than the level recorded on day 28 after the second shot. In addition, the findings brought on evidence showing that longer intervals between the third dose and the second dose result in higher antibody levels.


Seropositive rates in all dose groups were above 90.0% on day 28 after both the second and third doses. The severity of solicited local and systemic adverse reactions reported within 28 days after the third dose were grade 1 to grade 2 in all vaccination cohorts, and no serious adverse reactions were considered as related to the vaccination. A lower adverse reaction rate was observed after the third dose compared to the previous two-dose schedule.

This study is part of the ongoing phase II clinical trial in China, which started on May 3, 2020. This study is a placebo-controlled, double-blind phase II trial in adults aged 18 to 59 years old. The participants were randomly assigned to one of four groups of equal size, each with a different schedule to receive a third dose, 28 days or 6 months after two two-dose regimens, either 14 or 28 days apart. The immunization schedule of three-dose regime for four arms were: (1) days 0, 14, 42; (2) days 0, 14, 254; (3) days 0, 28, 56; and (4) days 0, 28, 268. 

In the discussion section, the authors proposed that a booster shot after a two-dose vaccination schedule of CoronaVac® may be necessary; however, policy makers must also consider factors such as the country’s epidemic situation, risk of infection, vaccine supply, etc. At this time, rather than promoting the use of a booster shot, priority should be given to increasing coverage of a two-dose vaccination with CoronaVac®.


[1] Immunogenicity and safety of a third dose, and immune persistence of CoronaVac vaccine in healthy adults aged 18-59 years: interim results from a double-blind, randomized, placebo-controlled phase 2 clinical trial. doi:



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


Safe Harbor Statements

This press release may include certain statements that are not descriptions of historical facts, but are forward-looking statements. These statements are made under the “safe harbor” provisions of the U.S. Private Securities Litigation Reform Act of 1995. These forward-looking statements can be identified by terminology such as “will,” “expects,” “anticipates,” “future,” “intends,” “plans,” “believes,” “estimates” and similar statements. Forward-looking statements involve risks, uncertainties and other factors that could cause actual results to differ materially from those contained in any such statements. In particular, the outcome of any litigation is uncertain, and the Company cannot predict the potential results of the litigation it filed or filed against it by others. Additionally, the triggering of a shareholder rights plan is nearly unprecedented, and the Company cannot predict the impact on the Company or its stock price as a result of the trigger of the rights plan.




Sinovac Biotech Ltd.

Helen Yang

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ICR Inc.

Bill Zima

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