Abstract
BACKGROUND: In Canada, mortality due to SARS-CoV-2 disproportionately impacted residents of nursing homes (NH). In November 2021, NH residents in the Canadian province of Manitoba became eligible to receive three doses of mRNA vaccine but coverage with three doses has not been universal. The objective of this study was to compare the protection from infection conferred by one, two, and three doses of COVID-19 mRNA vaccine compared to no vaccination among residents of nursing homes experiencing SARS-CoV-2 outbreaks. METHODS: Infection Prevention and Control reports from 8 rural nursing homes experiencing outbreaks of SARS-CoV-2 between January 6, 2022, and March 5, 2022, were analyzed. Attack rates and the number needed to vaccinate (NNV) were calculated. RESULTS: SARS-CoV-2 attack rate was 65% among NH residents not vaccinated, 58% among residents who received 1-2 doses of mRNA COVID-19 vaccine, and 28% among residents who had received 3 vaccine doses. The NNV to prevent one nursing home resident from SARS-CoV-2 infection during an outbreak was 3 for a vaccination with 3 doses and 14 for 1-2 doses of COVID-19 mRNA vaccine. The superiority of receiving the third dose was statistically significant compared to 1-2 doses (Chi-Squared, p < 0.00001). CONCLUSIONS: Nursing home residents who received three doses of COVID-19 mRNA vaccine were at lower risk of SARS-CoV-2 infection compared to those who received 1-2 doses. Our analyses lend support to the protective effects of the third dose of mRNA vaccine for NH residents in the event of a SARS-CoV-2 outbreak.