BEIJING, July 27 (Reuters) – Antibodies triggered by Sinovac Biotech’s COVID-19 vaccine (SVA.O) fell below a key threshold around six months after a second dose for most recipients, although that a third stroke had a strong recall effect, according to a laboratory study.
Chinese researchers reported the results of a study of blood samples from healthy adults aged 18 to 59 in an article published on Sunday, which was not peer reviewed. .
Among participants who received two doses, two or four weeks apart, only 16.9% and 35.2% respectively still had neutralizing antibodies above what the researchers consider to be a detectable threshold six months later. the second injection, according to the document.
These 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.
The researchers said it was not clear how the decrease in antibodies would affect the effectiveness of the shot, as scientists have yet to accurately determine the threshold for antibody levels for a vaccine to prevent. disease.
“In the short to medium term, making sure more people follow the current two-dose schedule of CoronaVac should be the priority,” the newspaper said.
Indonesia and Thailand have already agreed to give a third injection of Moderna and Pfizer respectively to some people fully vaccinated with the Sinovac vaccine, amid concerns about its effectiveness against the more transmissible Delta variant of the coronavirus.
Turkey had started offering a third dose of Sinovac or Pfizer to some people who received Sinovac injections.
By the end of June, Sinovac had delivered more than a billion doses of the vaccine, a major vaccination tool in China, Brazil, Indonesia and Chile.
Philippine Health Secretary Francisco Duque said on Tuesday that there was no recommendation yet from the country’s vaccine expert group on giving a booster, but experts are discussing the possibility .
The study also reported that participants in some cohorts who received a third dose of Sinovac vaccine around six months after the second showed an approximately 3-5-fold increase in antibody levels after an additional 28 days, compared to at levels seen four weeks after the second stroke.
The researchers warned that the study did not test the effect of antibodies against more transmissible variants, and that more research was needed to assess how long the antibodies last after a third injection.
The study was conducted by researchers from the disease control authorities of Jiangsu Province, Sinovac and other Chinese institutions.
Reporting by Roxanne Liu and Ryan Woo in Beijing, Neil Jerome Morales in Manila. Editing by Mark Potter, Miyoung Kim and Raju Gopalakrishnan
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