BACKGROUND: Vaccination campaigns were rolled out primarily to limit the impact of COVID-19 on severe health outcomes, including mortality.

AIM: We aimed to estimate the number of averted deaths by COVID-19 vaccination in the Belgian population aged 65 years and older, between January 2021 and January 2023.

METHODS: Nationwide data on COVID-19 infections, vaccine administrations and all-cause mortality were individually linked. We estimated Vaccine Effectiveness against COVID-19 mortality (VE) among persons having received a vaccine dose in the last 6 months, using a Cox proportional hazards model adjusted for age, sex, time since vaccination, previous infection, underlying health conditions, province and income. COVID-19 death was defined as a person with a laboratory-confirmed SARS-CoV-2 infection who died within a specified interval. Based on obtained VE estimates, vaccine coverage and national COVID-19 mortality data, we estimated the number of averted deaths.

RESULTS: We estimated VE (confidence interval (CI)) at 0-59 days after vaccination, for 65-79 year and ≥ 80 year-olds respectively, at 81.9 % (CI 78.1 %-85.1 %) and 74.7 % (CI 71.2 %-77.7 %) during Alpha, at 90.5 % (CI 88.8 %-91.9 %) and 91.4 % (CI 90.4 %-92.4 %) during Delta and at 84.0 % (CI 81.8 %-85.9 %) and 74.5 % (CI 72.4 %-76.5 %) during Omicron period. Among the Belgian population aged 65 years and older, we estimated 12,806 deaths averted (CI 11,633-13,982), representing a 54 % reduction (CI 51 %-56 %) in the expected deaths (without vaccination). During the Delta period COVID-19 deaths were reduced by 68 %, during Omicron by 54 % and during Alpha by 31 %.

DISCUSSION: Vaccinating against COVID-19 reduced deaths by 54 % among the Belgian population aged 65 years and older, underscoring the importance of COVID-19 vaccines in reducing mortality.