A large study of nearly 14 million children in England found that COVID-19 infection increases the risk of rare heart and blood vessel issues more than vaccination. The research shows vaccination is safer and sometimes protective against these complications. These findings strengthen evidence supporting vaccination for children during the pandemic.
The largest study to date, involving nearly 14 million children under 18, analyzed data from England's National Health Service (NHS) from January 2020 to December 2021. Led by Angela Wood at the Cambridge HDR UK Regional Network, the team compared risks after first COVID-19 infections and Pfizer/BioNTech vaccinations. During the latter half of this period, 3.9 million children received their first dose of the vaccine, while 3.4 million were diagnosed with a first infection.
Key findings highlight elevated risks post-infection. For children aged 5 to 18, there were more than 17 extra cases per 100,000 of inflammatory conditions like Kawasaki disease in the six months after infection, compared to nearly 2 fewer cases after vaccination. For myocarditis, inflammation of the heart muscle, infection led to more than 2 extra cases per 100,000, versus less than 1 extra after vaccination—making the risk more than twice as high after infection.
Reports of COVID-19 causing myocarditis emerged as early as April 2020. Vaccine-related myocarditis reports began in December 2020, mainly mild cases in young men who recovered quickly. This side effect drew significant media attention and delayed routine UK vaccination of young children until April 2022.
“I want to stress that these serious complications are really rare in children and young people overall,” says Wood. “But we can see that the risk was generally higher after a covid-19 infection than after a vaccination.”
The study has limitations: it does not indicate full recovery from complications, and many mild infections went undiagnosed due to limited testing later on. “However, despite those limitations, the scale of the data and the comprehensive linkage across all the NHS data gives us quite strong confidence in our overall conclusions today,” Wood adds.
William Whiteley at the University of Edinburgh notes that findings may not apply to current virus strains, given evolving immunity. Team member Pia Hardelid at University College London emphasizes the need for ongoing research, as responses to boosters and reinfections differ now.
The study is published in The Lancet Child and Adolescent Health (DOI: 10.1016/S2352-4642(25)00247-0).