Effectiveness and Duration of Protection of a Fourth Dose of Coronavirus Disease 2019 Messenger RNA Vaccine Among Long-term Care Residents in Ontario, Canada Journal Articles uri icon

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  • Abstract We estimated the effectiveness of a fourth dose of messenger RNA coronavirus disease 2019 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.


  • Grewal, Ramandip
  • Nguyen, Lena
  • Buchan, Sarah A
  • Wilson, Sarah E
  • Costa, Andrew
  • Kwong, Jeffrey C

publication date

  • April 18, 2023