Therapy Areas: Vaccines
Chinese lab study indicates that antibodies from Sinovac's COVID-19 vaccine fade after about six months
27 July 2021 -

A lab study in China has revealed that antibodies triggered by Chinese biopharmaceutical company Sinovac Biotech's (Sinovac) (Nasdaq:SVA) COVID-19 vaccine declined below a key threshold from around six months after a second dose for most recipients, although a third shot had a strong booster effect, Reuters news agency reported on Tuesday.

This study was conducted by researchers at disease control authorities in Jiangsu province in China, Sinovac and other Chinese institutions.

Chinese researchers reported these findings from a study of blood samples from healthy adults aged between 18-59 in a paper published on 25 July 2021, which has not been peer reviewed.

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 paper said.

Those readings were based on data from two cohorts involving more than 50 participants each, while the study gave third doses of the vaccine or placebo to a total of 540 participants.

Researchers said it was unclear how the decrease in antibodies would affect the shot's effectiveness, since scientists have yet to figure out precisely the threshold of antibody levels for a vaccine to be able to prevent the disease.

The study also showed 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.