Prospective Cohort Study Published in Vaccines Quantifies Incremental Effectiveness of a Second Dose of SINOVAC Varicella Vaccine, Live

BEIJING, China, July 31, 2026 — SINOVAC announced that a large-scale prospective cohort study evaluating the effectiveness of itsvaricella vaccine, live has been published in the peer-reviewed journal Vaccines. Led by the Anhui Provincial Center for Disease Control and Prevention (Anhui CDC), in collaboration with municipal and county CDCs and SINOVAC, the three-year study provides real-world evidence supporting the effectiveness of SINOVAC's varicella vaccine, live in children and quantifies the significant additional protection provided by a second dose.

The study is the first large-scale prospective real-world effectiveness evaluation of SINOVAC's varicella vaccine, live since its launch and the first prospective cohort study in Anhui Province to quantify the incremental effectiveness of a second dose. The findings provide evidence to support optimization of two-dose varicella vaccination strategy and catch-up vaccination among school-aged children.

More Than 47,000 Children Contributed Over 125,000 Person-Years of Follow-up

Conducted between July 2022 and August 2025, the study enrolled children aged 1–12 years from five regions in Anhui Province.

Children aged 1–3 years were followed to compare varicella incidence between those who received one dose of SINOVAC's varicella vaccine, live and unvaccinated children. Among children aged 4–12 years, researchers compared the incidence of varicella between those who received two doses (with SINOVAC's varicella vaccine, live administered as the second dose) and those who had received only one dose of varicella vaccine, live.

Participants were actively followed every three months, with vaccination and disease records verified through the Chinese CDC Information System and the Anhui Immunization Program Information Management System. Only varicella cases occurring at least 42 days after vaccination were included in the effectiveness analysis.

The final analysis included 50,054 analyzable participant-periods, contributing 125,351.5 person-years of follow-up. The mean follow-up duration was 30 months.

Study Demonstrates Strong Protection and Additional Benefit of a Second Dose

Among children aged 1–3 years, one dose of SINOVAC's varicella vaccine, live demonstrated an adjusted vaccine effectiveness (VE) of 79.1% (95% confidence interval [CI]: 42.8%–92.4%) compared with unvaccinated children. The point estimate was similar to the 80.2% efficacy observed in a previous Phase III trial of the same SV-1 vaccine in children aged 1–4 years.

Among children aged 4–12 years, who had already received one dose of varicella vaccine, live, a second dose of SINOVAC's varicella vaccine, live provided an incremental vaccine effectiveness (VE) of 65.0% (95% CI: 41.9%–78.9%).

Age-stratified analyses showed incremental VE of 60.1% among children aged 4–6 years and 72.7% among those aged 7–12 years. Both estimates were statistically significant.

Disease incidence decreased as the number of vaccine doses increased, from 1.38 cases per 1,000 person-years among unvaccinated children to 0.96 after one dose and 0.44 after two doses.The age-specific adjusted analyses provided the primary estimates of vaccine effectiveness.

In cumulative analyses from the start of cohort surveillance, the estimated incremental VE was 59.3% at 12 months, 70.1% at 24 months, and 65.0% at 36 months. Sensitivity analyses further supported the robustness of the findings.

Supporting Evidence-Based Immunization Strategy

The study suggests that one dose of SINOVAC's varicella vaccine, live provides substantial protection for young children. As children enter daycare and school and their exposure risk increases over time, a second dose offers additional protection against varicella for those who have already completed the primary vaccination.

The findings provide real-world evidence relevant to the implementation and optimization of two-dose varicella vaccination strategies, catch-up vaccination among school-aged children, and the prevention and control of varicella in school settings.

SINOVAC will continue collaborating with disease prevention and control institutions, universities, and healthcare organizations to generate post-marketing evidence on vaccine effectiveness, safety, and immunization strategies, contributing to evidence-based disease prevention and public health decision-making.

About SINOVAC's Varicella Vaccine, Live

SINOVAC's live attenuated varicella vaccine is manufactured using the company's proprietary SV-1 human diploid cell substrate. The vaccine received WHO prequalification in 2022 and remains on WHO’s current list of prequalified vaccines. Additional statements regarding formulation, manufacturing features, and global supply should be presented in accordance with the latest approved product information and verified company data.

About the Publication

Xuan K, Li T, Zha Z, et al. Incremental Effectiveness of a Second Varicella Vaccine in Children: A Prospective Cohort Study in Anhui, China. Vaccines. 2026;14:544.

Disclaimer

This press release summarizes findings from a published scientific study and is intended for informational purposes only. It does not replace professional medical advice or individual vaccination recommendations. Vaccination should be administered in accordance with local immunization policies, the approved product labeling, and the guidance of qualified healthcare professionals.

About SINOVAC

Sinovac Biotech Ltd. (SINOVAC) is a global biopharmaceutical company headquartered in China. Guided by its mission to “Supply Vaccines to Eliminate Human Diseases,” the Company is dedicated to the research, development, manufacturing and supply of vaccines and related biological products, providing vaccine products and related solutions for disease prevention and control worldwide.

SINOVAC has a diversified vaccine portfolio across multiple disease areas, including influenza, viral hepatitis, varicella, hand, foot and mouth disease (HFMD), poliomyelitis, rabies, tetanus, and pneumococcal disease. Three of SINOVAC's vaccines have been prequalified by the World Health Organization: the inactivated hepatitis A vaccine Healive®, the Sabin-strain inactivated poliomyelitis  vaccine (sIPV), and the live attenuated varicella vaccine.

SINOVAC has extensive experience in vaccine research, development and commercialization for emerging infectious diseases and public health emergencies. The Company initiated vaccine R&D in response to major public health threats, including SARS, H5N1, H1N1, and COVID-19, and developed the world's first inactivated SARS vaccine (with Phase I clinical trials completed), China's first inactivated pandemic influenza vaccine against H5N1 (Panflu®), the world's first H1N1 influenza vaccine (Panflu.1®), and CoronaVac®, the world's most widely used inactivated COVID-19 vaccine. Beyond its marketed portfolio, SINOVAC continues to advance its R&D pipeline, spanning combination vaccines, recombinant protein vaccines, mRNA technologies, antibody-based products, and other next-generation technologies and product platforms, while expanding its capabilities in disease prevention and biopharmaceuticals.

With a long-standing commitment to innovation and global health, SINOVAC continues to deepen collaboration with research institutions, international organizations, and local partners while expanding its global presence. Through technological collaboration, localized production, and industrial partnerships, the Company aims to improve access to high-quality vaccines across regions, better address local disease prevention and healthcare needs, and strengthen preparedness for future public health challenges.

For more information, please see the Company's website at www.sinovac.com.