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The problem
Intervention: COVID-19 vaccination with BNT162b2 or CoronaVac vaccines, delivered as partial series (1 dose) or complete primary series (2 doses)
Who it was tested with: Children aged 3 to 4 years in Brazil during the Omicron phase (epidemiological weeks 31-52 of 2022 and weeks 1-13 of 2023).
Children or communities are compared with a group that did not receive the intervention, or followed over years. This is the design that best separates what the intervention did from everything else that changed.
"This nationwide population-based cohort study assessed incidence rate ratios for hospitalization due to COVID-19-associated severe acute respiratory syndrome, invasive ventilatory support, and death among children aged 3 to 4 years, according to vaccination status (unvaccinated, 1 dose, or 2 doses), during 2022-2023." The design uses national health registries to compare outcomes across clearly defined vaccination status groups, meeting criteria for an experimental/quasi-experimental approach with comparison groups.
Direct vaccine comparison not feasible due to very low BNT162b2 coverage (2% of children). The study was observational rather than randomized, and effectiveness estimates may vary with different variants or over time.
Across countries and designs
9 studies · 6 countries
