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

Miguel A Hernán1, Alejandro Álvaro-Meca2,3, María J Calvo-Alcántara4

  • 1From the CAUSALab, Departments of Epidemiology and Biostatistics, Harvard T.H. Chan School of Public Health, Boston, MA.

The Pediatric Infectious Disease Journal
|December 16, 2025
PubMed

Insights

COVID-19 mRNA vaccines showed small risks and benefits in children aged 6-17. The study found minimal impact on hospitalizations and inflammatory syndromes, with no myocarditis cases in younger children.

Area of Science:

  • Pediatric Infectious Diseases
  • Vaccinology
  • Public Health

Background:

  • The benefit-risk profile of coronavirus disease 2019 (COVID-19) mRNA vaccination in children requires further clarification.
  • Evaluating the impact on hospitalization, myocarditis, and multisystem inflammatory syndrome in children (MIS-C) is crucial for pediatric populations.

Purpose of the Study:

  • To assess the effects of mRNA vaccines on COVID-19 hospitalization, myocarditis/pericarditis, and MIS-C in children aged 6-17 years.
  • To quantify the effectiveness and safety of COVID-19 vaccination in different pediatric age groups.

Main Methods:

  • A retrospective cohort study using linked health system registries in Madrid, Spain.
  • Matched 183,273 vaccinated children (6-11 yrs) and 277,561 vaccinated children (12-17 yrs) with unvaccinated controls.
  • Compared 240-day risks for adverse events and COVID-19 hospitalization using bootstrapping for confidence intervals.

Main Results:

  • In children 6-11 years, vaccine effectiveness against COVID-19 hospitalization was 9.0% (95% CI: -36 to 49), and for MIS-C was 27.0% (-54 to 76). No myocarditis/pericarditis cases were observed.
  • In children 12-17 years, effectiveness against COVID-19 hospitalization was 45% (18-72), and for MIS-C was 42% (-31 to 83). The risk ratio for myocarditis/pericarditis was 1.09 (0.60-1.70).
  • Risk differences for COVID-19 hospitalization and MIS-C were small across both age groups.

Conclusions:

  • The risks and benefits associated with COVID-19 mRNA vaccines were minimal in the general pediatric population aged 6-17.
  • The study suggests a generally favorable safety profile for COVID-19 vaccination in children, with limited impact on key health outcomes.
Abstract

Keywords:
observational studytarget trial emulationvaccine effectivenessvaccine safety

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