Author Correction: Effectiveness of mRNA COVID-19 vaccine booster doses against Omicron severe outcomes

BackgroundTo inform planning for further booster doses of COVID-19 vaccines, we estimated the effectiveness of monovalent mRNA vaccines against Omicron-associated severe outcomes in adults over time.MethodsWe used a test-negative design and multivariable logistic regression to estimate vaccine effectiveness (VE; 2, 3, or 4 doses compared to unvaccinated individuals) and marginal effectiveness (3 or 4 doses compared to 2 doses) against Omicron-associated hospitalization or death among community-dwelling adults aged ≥50 years who were tested for SARS-CoV-2 between January 2, 2022 and October 1, 2022 in Ontario, Canada, stratified by age group and time since vaccination. We also compared VE during periods of Omicron BA.1/BA.2 and BA.4/BA.5 sublineage predominance.ResultsWe included 11,160 cases of Omicron-associated severe outcomes and 62,880 test-negative symptomatic controls. Depending on the age group, compared to unvaccinated individuals, VE was 91-98% 7-59 days after a third dose, waned to 76-87% after ≥240 days, was restored to 92-97% 7-59 days after a fourth dose, and waned to 86-89% after ≥120 days. Trends in marginal effectiveness were consistent with VE estimates. VE was lower during the BA.4/BA.5-predominant period compared to the BA.1/BA.2-predominant period based on the same intervals since vaccination.ConclusionOur findings suggest that 1 or 2 booster doses of monovalent mRNA COVID-19 vaccines initially restored very strong protection against Omicron-associated severe outcomes in all age groups, but VE subsequently declined over time with some age-related differences, and particularly so during a period of BA.4/BA.5 predominance.