Abstract
ObjectivesThe COVID-19 pandemic required rapid development of vaccines within a short period of time which did not allow to assess vaccine effectiveness (VE) in the long-term. MethodsA computerized literature search was undertaken to identify eligible studies, with no language restrictions, published between 1 December 2020 and 30 June 2023. ResultsOut of a total of 27,597 publications, 761 studies were included. Early VE of 87.2% decreased to 55.1% after 9 months among populations fully immunized not only with mRNA (proxy mRNA) vaccines, and 66.3% decreased to 23.5% in populations immunized exclusively with non-mRNA vaccines. Protection against severe COVID-19 declined to 80.9% for proxy mRNA vaccines and 67.2% for non-mRNA vaccines. Omicron variants significantly diminished VE. Within 6-8 months of receiving a single booster of an mRNA vaccine, VE declined to 14.0% and 67.7% for any and severe COVID-19, respectively. Multiple mRNA booster doses restored protection that declined to 29.5% and 70.6% for any and severe COVID-19, respectively, within 5-7 months. ConclusionOutcomes of this meta-regression underscore the evolving nature of COVID-19 in response to vaccination, dosing schedules, and emerging variants, and provide crucial insights for public health interventions and vaccination strategies.
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