Effectiveness and duration of protection of a fourth dose of Coronavirus disease 2019 messenger RNA vaccine among long-term care residents in Ontario, Canada

We estimated the effectiveness of a fourth dose of mRNA COVID-19 vaccine against Omicron infections and severe outcomes over time among long-term care residents in Ontario, Canada. Fourth doses provide additional protection against Omicron-related outcomes, but the protection wanes over time, with more waning seen against infection than severe outcomes.

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Grewal R, Nguyen L, Buchan SA, Wilson SE, Costa AP, Kwong JC. J Infect Dis. 2023; 227(8):977–80. Epub 2022 Dec 3.

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