How effective are COVID-19 mRNA vaccines in children?

Immunization with COVID-19 mRNA vaccines is safe and provides a small protective benefit in children aged 6‒17 years, as shown in a Spain study.

“[B]oth the risks and benefits of COVID-19 mRNA vaccines were small among the general population of children at the time the initial recommendations were made,” the researchers said.

“These findings may help inform future updates to paediatric vaccination policies and suggest that, rather than universal recommendations, an individualized approach to COVID-19 vaccination for children may be preferred,” they added.

The research team identified eligible children 6‒17 years of age by linking the Madrid Health System Registry with three databases of the Madrilenian Health Service (primary care, hospital admissions, and pharmacy). Then, they matched children receiving an mRNA vaccine with five controls and compared 240-day risks for vaccines and controls.

All analyses were conducted by age group: 6‒11 and 12‒17 years. Effectiveness was defined as 1 minus the risk ratio.

In 183,273 vaccinated and 916,365 control participants aged 6‒11 years, the estimated 240-day risk of COVID-19 hospitalization was 11.5 (21 events) and 12.7 (116 events) per 100,000 (risk difference, ‒1.2 per 100,000, 95 percent confidence interval [CI], ‒6.6 to 4.0). Vaccination had an estimated effectiveness of 9.0 percent (95 percent CI, ‒36 to 49). [Pediatr Infec Dis J 2026;45:e121-e124]

The risk difference of multisystem inflammatory syndrome in children (MIS-C) was ‒1.4 per 100,000 (95 percent CI, ‒4.7 to 2.3), with an estimated effectiveness of 27.0 percent (95 percent CI, ‒54 to 76). Cases of myocarditis or pericarditis did not occur.

In 277,561 vaccinated and 1,387,805 control participants aged 12–17 years, the estimated 240-day risk of COVID-19 hospitalization was 6.5 (18 events) and 11.8 (164 events) per 100,000 (risk difference, ‒5.3 per 100,000, 95 percent CI, ‒9.0 to ‒2.0). The estimated effectiveness of mRNA vaccines was 45 percent (95 percent CI, 18‒72).

The risk difference of MIS-C was ‒1.3 per 100,000 (95 percent CI, ‒3.0 to 0.8). The estimated effectiveness of vaccines was 42 percent (95 percent CI, ‒31 to 83), and the risk ratio of myocarditis or pericarditis for vaccinated vs control participants was 1.09 (95 percent CI, 0.60‒1.70).

COVID-19 hospitalization

“Our estimates of risks of COVID-19 hospitalizations were under 13 per 100,000 children,” the researchers said.

“These estimates are lower than those from previous publications, some of which reported risks between 40 and 60 per 100,000 US children 5–17 years of age during the period of our study,” they added. [MMWR Morb Mortal Wkly Rep 2021;70:1255-1260; MMWR Morb Mortal Wkly Rep 2020;69:1081-1088; MMWR Morb Mortal Wkly Rep 2021;70:1249-1254]

This discrepancy could be potentially explained by the inability to distinguish between hospitalizations “for” and “with” COVID-19 in previous studies. For instance, records from a US hospital during the first year of the pandemic indicated that nearly half of hospitalizations of children with COVID-19 were not caused by the infection itself. [Hosp Pediatr 2021;11:e151-e156]

“The databases used in our study allow to distinguish between hospital admissions in which COVID-19 was or was not the primary reason for hospitalization,” the researchers said.

“This classification is carried out for all hospital admissions by clinical documentation specialists according to standardized procedures,” they added.