Sinovac COVID-19 vaccine. Photo: VCG

The third dose of Sinovac's inactivated vaccine would increase antibody response tenfold in a week, a second-phase clinical trial showed, but the large-scale adoption of a third dose still needs more studies. 

Yin Weidong, the head of China's vaccine producer Sinovac, told China Central Television on Saturday that the company recently completed the second phase clinical trial, which showed that when volunteers who had received two doses of Sinovac's COVID-19 vaccine received a third shot after three and six months, the antibody response inside their bodies could soar tenfold in a week and twenty-fold in 15 days.

However, Sinovac will conduct more thorough and longer periods of research to determine the best time to receive a booster for the general public, Yin said. 

"After completing the two shots, our body has already produced an immune memory. As for when the third shot will be needed, please give researchers more time to study it," Yin said. 

Asked if Sinovac has new vaccines to protect against mutated variants, Sinovac spokesperson Liu Peicheng was quoted by Chinanews.com on Saturday as saying that studies on the immunogenicity of the variant strains are being carried out.

Liu said inactivated vaccines have a mature process route. In theory, changing the strain does not require this route to be changed. Sinovac will conduct small-scale trials to confirm whether the existing process route can achieve vaccine production that is effective against the new mutated variants. 

There have been discussions over whether inoculated people will require a booster in the future. Chinese health authorities said they will determine when to administer booster shots for COVID-19 based on analysis of early vaccinated groups to combat the threat of mutant strains.

Data from people vaccinated six months ago is now being analyzed, and preliminary results showed that the antibody levels for about half of them are still good, Shao Yiming, a leading physician and immunologist from the Chinese Center for Disease Control and Prevention, told media earlier. 

"With the support of scientific data, we will determine when people who have been vaccinated for a long time should be given a booster shot," he said.

Global Times