Sinovac vaccine Photo: VCG

The latest real-world observation data in Chile has shown that the third shot of the CoronaVac inactivated COVID-19 vaccine developed by Sinovac can clearly increase the strength of protection. Specifically, increased effectiveness against COVID-19 14 days after the booster shot can reach 80.2 percent, up from 56 percent, while increasing the effectiveness against hospitalization by 88 percent, up from 84 percent.

Sinovac confirmed the necessity of the booster shot, while denying the claim by some Western and Hong Kong media reports that the booster jab is less effective if administered more than six months after the completion of the second dose.

Previous studies have shown a significant increase in neutralizing antibody levels after taking a booster shot eight months after the second shot, Sinovac told the Global Times. Studies also showed that a booster jab given earlier or later than eight months after the full course - such as the sixth month or 12th month - is also effective in heightening the protection. 

The World Health Organization (WHO) has suggested that a booster dose is immunogenic and will be needed for older adults over 60 who have completed two doses of vaccination. CoronaVac is also recognized as a safe choice as a booster for people with serious immune deficiency. 

By the end of September 2021, the cumulative global supply of CoronaVac had reached 2 billion doses, with 1.6 billion doses administered, making it the most widely available COVID-19 vaccine globally.

Evidence suggests that neutralizing antibodies against SARS-CoV-2 induced by all types of vaccines wane over time, which may decrease their effect against COVID-19 and its consequences.

The effectiveness assessments performed by Chile's Ministry of Health showed a sharp decrease in effectiveness, specifically within the group immunized with inactivated vaccines early on, said the developer.

Sinovac said the research data shows that all adverse reactions were grade 1 or 2 after the booster injection, and no serious adverse reactions were directly caused by the vaccine.

Booster injections are being promoted in many countries at the moment, and the interval between the second and third episodes may vary by age group, comorbidities and local virus prevalence.

Overall, administration of a third dose of an inactivated virus vaccine can boost the immune response and raise a better neutralization breadth and long-lasting response in warding off COVID-19, according to the data after researchers analyzed 171 complex structures of SARS-CoV-2 neutralizing antibodies.

Since December 2020, CoronaVac has been approved for emergency use in more than 50 countries and regions around the world. Its safety and effectiveness have been confirmed in real studies, and it has been included in the WHO emergency use list. Since September, CoronaVac has been used to vaccinate minors in Chile, Cambodia, Indonesia and Malaysia.