China Preliminary Study: Sinovac COVID-19 Vaccine Antibodies Decline After About 6 Months

The antibody triggered by Sinovac Biotech’s COVID-19 vaccine decreased below a key threshold starting about six months after a second dose for most recipients, although a third injection had a strong stimulating 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the results of a study of blood samples from healthy adults aged 18 to 59 in an article published on Sunday, which was not peer reviewed.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 to four weeks apart, only 16.9% and 35.2%, respectively, still had neutralizing antibodies above what the researchers consider a detectable cutoff level six months after the second injection, according to the article.

These readings were based on data from two groups of more than 50 participants each, while the study administered third doses of the vaccine or placebo to a total of 540 participants.

The researchers noted that It is not known how the reduction in antibodies affects the effectiveness of the vaccine, as scientists have not yet precisely determined the threshold for antibody levels for a vaccine to prevent the disease.

“In the short to medium term, the priority should be to ensure that more people complete the current two-dose CoronaVac program,” the document said.

Indonesia and Thailand have already agreed to give a third dose 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 had been vaccinated with Sinovac.

Until the end of June, Sinovac had provided more than a billion doses of the vaccine, one of the main vaccination tools in China, Brazil, Indonesia, Uruguay and Chile.

Philippine Health Secretary Francisco Duque said on Tuesday that the country’s vaccine expert group had yet to recommend a booster, but experts are debating the possibility.

The study also noted that Participants in some groups who received a third dose of Sinovac vaccine about six months after the second showed a 3-5-fold increase in antibody levels after an additional 28 days, compared to levels seen four weeks after the second injection.

The researchers warned that the study did not test the effect of antibodies against the more transmissible variants and that more research is needed to assess how long 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.

(With information from Reuters)

KEEP READING: