Effectiveness and Safety of COVID-19 mRNA Vaccines in Children 6–17 Years Old: A Population-based Study in Madrid

BACKGROUND: The benefit-risk of coronavirus disease 2019 (COVID-19) vaccination in children remains unclear. We evaluated the effects of mRNA vaccines on COVID-19 hospitalization, pericarditis/myocarditis, and MISC-C in children 6-17 years old. METHODS: The Madrid Health System Registry was linked with 3 databases of the Madrilenian Health Service (primary care, hospital admissions, and pharmacy) to identify eligible children 6-17 years of age. We matched children receiving an mRNA vaccine with 5 controls and compared 240-day risks for vaccines and controls, with bootstrapping to obtain 95% confidence intervals. Effectiveness was defined as 1 minus the risk ratio. All analyses were conducted by age group (6-11 and 12-17 years). RESULTS: In 183,273 vaccinated and 916,365 controls 6-11 years old, the estimated risk difference (95% CI) of COVID-19 hospitalization was -1.2 per 100,000 (-6.6 to 4.0) for vaccinated versus controls; effectiveness 9.0% (-36 to 49). The risk difference of multisystem inflammatory syndrome in children was -1.4 per 100,000 (-4.7 to 2.3); effectiveness 27.0% (-54 to 76). No cases of myocarditis or pericarditis occurred. In 277,561 vaccinated and 1,387,805 controls 12-17 years old, the estimated risk difference of COVID-19 hospitalization was -5.3 per 100,000 (-9.0 to -2.0); effectiveness 45% (18-72). The risk difference of multisystem inflammatory syndrome in children was -1.3 per 100,000 (-3.0 to 0.8), effectiveness 42% (-31 to 83). The risk ratio of pericarditis/myocarditis for vaccinated versus controls was 1.09 (0.60-1.70). CONCLUSIONS: The risks and benefits of COVID-19 vaccines were small in a general population of children 6-17 years of age.