Antibodies generated by China’s Sinovac’s COVID-19 vaccine decrease below a key threshold six months after receiving the second dose. However, a third shot boosts the antibodies, a lab study has found.
The study involved two cohorts with over 50 participants each who had received two doses of Sinovac’s vaccine two and four weeks apart respectively while 540 participants either received the third dose of the vaccine or a placebo.
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According to the study, only 16.9% and 35.2% of the participants who received the two doses of Sinovac’s vaccine two and four weeks apart respectively had neutralizing antibodies above what researchers regard as a detectable threshold level six months after the second dose.
It states that it remains unclear how reduced antibodies would impact the effectiveness of Sinovac’s COVID-19 vaccine since scientists have not yet agreed on a single threshold of antibody levels for a vaccine to be able to prevent the Coronavirus infection.
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Moreover, participants who received a third dose of the Sinovac shot about six months after the two doses showed around a 3-5 fold increase in antibody levels after a month.
On the other hand, Indonesia and Thailand have already approved a third booster dose of Moderna or Pfizer for people fully vaccinated with Sinovac’s COVID-19 vaccine amid concerns over its effectiveness against the highly transmissible Delta variant. Meanwhile, Turkey has started administering the third dose of either Sinovac or Pfizer to people vaccinated with Sinovac’s vaccine.
