Reviewed by Dr. Michael Payne, MD; London Health Sciences Centre
This study estimated the effectiveness of a fourth dose of monovalent mRNA COVID-19 vaccine against Omicron infections and severe outcomes among long-term care residents in Ontario, Canada. Compared with individuals who had received a third dose ≥84 days earlier, the marginal effectiveness of a fourth dose received <84 days earlier was 23% against infection, 36% against symptomatic infection, and 37% against severe outcomes. Marginal effectiveness decreased over time, with negligible (<10%) additional protection against infection and symptomatic infection by 112–139 days and against severe outcomes after 168 days. When compared to unvaccinated individuals, protection from infection did wane significantly over time, but protection against severe outcomes was maintained at ≥168 days (74%). This data informs the potential need for a 6 month booster dose in higher risk populations, including elderly patients living in LTC.
The Journal of Infectious Diseases, Volume 227, Issue 8, 15 April 2023, Pages 977–980.