Coronavirus: fourth shot of Sinopharm vaccine won’t boost protection against Omicron, study finds

Sun Yat-sen University team says ‘urgent use’ of such inactivated vaccines as a fourth booster against variants of concern is ‘feasible but not ideal’

Their research, which has not been peer-reviewed, suggests immune response cannot be endlessly boosted and there will be a ‘turning point’ after repeated vaccination

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A third dose of the vaccine was found to be “the turning point” on immune response for most study participants. Photo: AFP

Published: 11:00am, 24 Feb 2022

Immunity wanes six months after three doses of the Sinopharm Covid-19 vaccine are given, but a fourth shot will not provide more protection against the Omicron strain, a study has found.

Researchers from Sun Yat-sen University in Guangzhou said their study suggested that “urgent use” of inactivated vaccines – like the Sinopharm one – as a fourth booster shot against variants of concern such as Omicron was “feasible but not ideal”.

Recombinant spike protein or mRNA vaccines based on the variants of concern would be good alternatives for a fourth booster, they said.

The study suggested that immune response could not be endlessly boosted and there would be a “turning point” after repeated vaccination.

“The timing for the plateau may vary depending on the nature of antigens and adjuvants. For the inactivated vaccines used in this study, the turning point is the third dose for most participants,” the researchers wrote.

“Strikingly, data in the current study indicated that neutralisation breadth was not further increased by the fourth dose, but even narrowed.”

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