Publication date: Jul 29, 2026
National population-based databases from large countries can provide real-world estimates of COVID-19 vaccine effectiveness. This analysis examined the effectiveness of BNT162b2 and CoronaVac against severe COVID-19-related outcomes in children aged 3 to 4 years during the Omicron phase of the pandemic in Brazil. 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 study period spanned epidemiological weeks 31-52 of 2022 and weeks 1-13 of 2023. Data on laboratory-confirmed COVID-19-related hospitalizations, clinical outcomes, and vaccination status were obtained from OpenDATASUS, and vaccination coverage was estimated using data from the Brazilian Ministry of Health COVID-19 vaccination dashboard. Among children aged 3 to 4 years completion of the primary series increased to 15% for CoronaVac and 2% for BNT162b2 during the study period, corresponding to 797,956 and 79,650 individuals receiving the second dose, respectively. A total of 963 children were hospitalized with COVID-19-associated severe acute respiratory syndrome. Vaccine effectiveness against hospitalization was 79. 0% (95% CI, 69. 9%-85. 4%) after partial vaccination and 49. 2% (95% CI, 32. 5%-61. 9%) after completion of the primary series (p
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| Concepts | Keywords |
|---|---|
| COVID-19 vaccines | |
| Inactivated vaccines | |
| mRNA vaccines | |
| Preschool child | |
| Vaccine effectiveness | |
| Vaccine efficacy |
Semantics
| Type | Source | Name |
|---|---|---|
| disease | MESH | COVID-19 |
| disease | MESH | severe acute respiratory syndrome |
| disease | MESH | death |