Effectiveness of BNT162b2 and mRNA-1273 vaccines against COVID-19 omicron variants in children aged 6–11 years in Taiwan

Although COVID-19 is typically less severe in children, pediatric infections contribute to transmission and severe disease, particularly in those with comorbidities. This study evaluates the vaccine effectiveness (VE) of BNT162b2 and mRNA-1273 against Omicron BA.2/BA.5 in Taiwan, an infection-naïve population at the time of vaccine introduction. This nationwide observational study utilized the National Health Insurance Research Database and the National Immunization Information System. We included children aged 6–11 years who completed a two-dose primary series between May and June 2022 or remained unvaccinated. Propensity score weighting (PSW) adjusted for age, sex, and health status. Outcomes included SARS-CoV-2 infection confirmed via emergency department (ED) visits or hospitalization, and moderate-to-severe COVID-19. VE was estimated using weighted logistic regression. Among 347,715 children, 115,449 received BNT162b2, 91,531 received mRNA-1273, and 140,735 were unvaccinated. Compared with unvaccinated children, adjusted VE against ED-confirmed infection was 58.8% (95% CI: 53.6%–63.4%) for BNT162b2 and 73.9% (95% CI: 69.3%–77.8%) for mRNA-1273. For moderate-to-severe disease, VE was 69.9% (95% CI: 58.0%–78.5%) for BNT162b2 and 75.5% (95% CI: 63.2%–83.6%) for mRNA-1273. Protection remained consistent across clinical subgroups. A two-dose primary series of BNT162b2 or mRNA-1273 provided substantial protection against moderate-to-critical COVID-19 and reduced ED-confirmed infections during the Omicron period. These results support the public health value of pediatric mRNA vaccination in preventing severe outcomes in settings with low prior infection rates. • mRNA vaccines cut severe COVID-19 risk in infection-naïve kids aged 6–11. • BNT162b2 and mRNA-1273 both effectively reduced emergency room visits. • High protection was maintained for children with underlying health conditions. • Results confirm the value of primary series vaccination during Omicron waves.