Abstract
AbstractIntroductionMonitoring of COVID-19 vaccine effectiveness (VE) is needed to inform vaccine policy. We estimated VE of primary vaccination, and first and second booster vaccination, against SARS-CoV-2 infection overall, and in four risk groups defined by age and medical risk condition, in the Delta and Omicron BA.1/BA.2 periods.MethodsVASCO is an ongoing prospective cohort study among vaccinated and unvaccinated Dutch adults. The primary endpoint was a self-reported positive SARS-CoV-2 test during 12 July 2021-6 June 2022. Participants with a prior SARS-CoV-2 infection, based on a positive test or serology, were excluded. We used Cox proportional hazard models with vaccination status as time-varying exposure and adjustment for age, sex, educational level, and medical risk condition. We stratified by Delta and Omicron BA.1/BA.2 periods, risk group, and time since vaccination.Results37,170 participants (mean age 57 years) were included. In the Delta period, VE <6 weeks after primary vaccination was 80% (95%CI 69-87) and decreased to 71% (65-77) after 6 months. VE increased to 96% (86-99) shortly after the first booster vaccination. In the Omicron period these estimates were 46% (22-63), 25% (8-39) and 57% (52-62), respectively. VE was 50% (34-62) <6 weeks after a second booster vaccination in participants aged ≥60 years. For the Omicron period, an interaction term between vaccination status and risk group significantly improved the model (p<0.001), with generally lower VEs for those with a medical risk condition.ConclusionsOur results show the benefit of booster vaccinations against infection, also in risk groups, although the additional protection wanes quite rapidly.SummaryThis prospective cohort study contributes to vaccine policy of COVID-19 by showing the benefit of booster vaccination in preventing SARS-CoV-2 infections, also in risk groups in which protection was generally lower, although the additional protection was rather short-lived.
Publisher
Cold Spring Harbor Laboratory
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