Barda N, Dagan N, Cohen C, et al. - Researchers herein investigated the effectiveness of a third dose of the BNT162b2 mRNA vaccine in preventing severe COVID-19 outcomes using the data repositories of Israel's largest healthcare organization.

• For inclusion in the third dose group, researchers identified 1,158,269 individuals as eligible.

• Following matching, 728,321 individuals were included in both the third dose and control groups.

• Compared with receiving only two doses at least 5 months ago, receipt of the third dose was linked with vaccine effectiveness (evaluated at least 7 days after the receipt) of 93% (231 events for two doses vs 29 events for three doses; 95% CI 88–97) for admission to hospital, 92% (157 vs 17 events; 82–97) for severe disease, and 81% (44 vs seven events; 59–97) for COVID-19-related death.

• Receipt of the third dose of the BNT162b2 mRNA vaccine was linked with induction of protection in individuals against severe COVID-19-related outcomes, compared with receiving only two doses at least 5 months ago.