are given, but a fourth shot will not provide more protection against the Omicron strain, a study has found.
The study suggested that immune response could not be endlessly boosted and there would be a “turning point” after repeated vaccination. At present, China’s booster campaign only involves a third dose. Booster shots can be vaccines using the same technology as previous doses, or a mix of two doses of an inactivated vaccine plus either a recombinant protein or vectored vaccine.
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