Effectiveness of BNT162B2 and CoronaVac vaccines in reducing COVID-19 severity among children aged 3-4 years in Brazil.
INTRODUCTION 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. METHODS 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. RESULTS 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 < 0.01). Effectiveness against invasive mechanical ventilation was 77.6% and 79.1%, respectively; no deaths occurred among fully vaccinated children. Direct comparisons between vaccines were not feasible because of the lower proportion of BNT162b2 recipients. CONCLUSIONS COVID-19 vaccination, predominantly based on the CoronaVac vaccine, was associated with a significant reduction in severe outcomes among children aged 3-4 years, providing robust evidence to support pediatric immunization strategies and public health efforts.