Antibodies from Sinovac's Covid-19 vaccine decline after about six months, booster helps

PETALING JAYA (July 27): Third booster shot of Covid-19 vaccine could help to increase immune response as a finding showed that antibodies induced by CoronaVac, a Covid-19 vaccine developed by China's Sinovac Biotech, declines below a key threshold about six months after the recipients took the second dose, reported Reuters. 

Citing a lab study by Chinese researchers, the news report among participants who received two doses, two or four weeks apart, only 16.9% and 35.2% respectively still had neutralising antibodies above what researchers regard as a detectable threshold level six months after the second shot

The finding is based on blood samples collected from healthy participants aged 18-59 and hasn't been peer-reviewed. A total of 540 people were given a third shot, but only the samples of 271 participants were included in the analysis, according to a statement of Sinovac on July 27, 2021.

The report said researchers are uncertain on how the reducing antibodies would affect the shot's effectiveness, as scientists are still figuring out the threshold for the level of the antibody to be effective in preventing the disease.

The study also said that participants in some cohorts who received a third dose of the Sinovac shot about six months after the second showed around a three to five fold increase in antibody levels after a further 28 days, compared with the levels seen four weeks after the second shot.

Meanwhile, Indonesia, Thailand and Turkey are planning to let the people who completed two shots of Sinovac vaccine to take a third dose of Covid-19 vaccine. 

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