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Results from an ongoing phase 2 clinical trial studying immunogenicity, safety, and immune persistence of CoronaVac ® show that while good immune memory is generated after the second dose, a third dose induces a stronger immune response, with an even lower adverse reaction rate after the third dose as compared to the second. A booster shot after a two-dose schedule is recommended, however, the focus should remain on increasing two-dose vaccination
with CoronaVac ®.

Article Summary

Sinovac announced the pre-print of a paper available on Medrxiv, 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.

The ongoing clinical trial in China randomly assigned participants into 4 groups with different schedules. Results demonstrate that while CoronaVac ® generates good immune memory after the second dose, a third dose given 6-8 months after the second induced a strong immune response with three to five times the increase in neutralizing antibody titers at day 28 after the third dose as compared to the second. Higher antibody levels were also
observed following longer intervals between the second and third dose.

Seropositive rates were above 90.0% and no serious adverse reactions were reported. The adverse reaction rate after the third dose was also lower compared with that of the previous two-dose schedule.

The authors proposed the necessity of a booster shot after a two-dose vaccination schedule of CoronaVac ®, however, this is contingent upon countries’ individual circumstances. Increasing coverage of a two-dose vaccination with CoronaVac ® should remain of utmost priority.

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SINOVAC Biotech Ltd. is a China-based biopharmaceutical company focusing on research, development, manufacturing, and commercialization of vaccines targeting human infectious diseases. The company boasts a vast product portfolio and its COVID-19 vaccine, CoronaVac ®, has been granted emergency use authorization or conditional marketing
authorization in over 50 countries or regions worldwide. Sinovac is developing various new products and sells vaccines both in China and internationally.

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(Source: Sinovac,21st July 2021)