Sinovac Covid-19 vaccine’s antibodies fade after 6 months, third shot could boost effect: Chinese study

Beijing — A lab study has discovered that the antibodies triggered by the Sinovac Covid-19 vaccine decline below a key threshold from around six months after the second dose. A third shot could be necessary for a strong boosting effect.

The study, which was conducted on blood samples from healthy adults aged between 18 and 59, was published in a paper on Sunday (Jul 25), although it has not been peer-reviewed.

Chinese researchers noted that the fully vaccinated participants who had followed the two- or four-week interval between each dose showed a 16.9 per cent and 35.2 per cent level of neutralizing antibodies above the threshold six months after the second dose.

The study consisted of two groups involving more than 50 participants each. A third dose was given to a total of 540 participants.

The participants who received the third dose about six months after the second experienced increased levels of neutralizing antibodies about three to five-fold compared to the levels observed four weeks after the second dose.

Researchers at disease control authorities in Jiangsu province, Sinovac and other Chinese institutions involved in the study noted that further research was needed to assess antibody duration after a third shot.

They also did not test the antibodies’ effect against more transmissible variants.

To date, about 72,000 people in Singapore have received at least one dose of the Sinovac vaccine, while about 17,000 have completed the vaccination process.

Health Minister Ong Ye Kung announced in Parliament on Jul 26 that if the country’s supply of 200,000 doses is insufficient, additional supplies can be purchased by private clinics.

The most comprehensive analysis of the Sinovac vaccine indicated a 51 per cent efficacy rate, compared to the estimated 90 per cent efficacy rate shown by the mRNA vaccines by Pfizer-BioNTech and Moderna. /TISG

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