Covid raises risk of heart issues in children more than vaccination

Evidence that children are better off getting vaccinated against COVID-19 than the infection became even worse during the pandemic. The largest study in history, involving nearly 14 million children, found that the risk of serious – but very rare – side effects affecting the heart and blood vessels was much higher after infection than after vaccination.

For example, among children aged 5 to 18 years, there were more than 17 additional cases per 100,000 of inflammatory conditions such as Kawasaki disease in the six months after first SARS-CoV-2 infection compared with other periods. Among first-time recipients of the Pfizer/BioNTech mRNA vaccine, there were nearly 2 fewer cases per 100,000.

Inflammation of the heart muscles, known as myocarditis, occurred in more than 2 additional cases per 100,000 people within six months of infection. There was less than 1 excess case among those vaccinated. In other words, the risk of myocarditis after infection was more than twice as high as after vaccination.

Reports of Covid-19 infections causing myocarditis have been published already in April 2020. After the start of vaccination in December of the same year, reports also began to appear about vaccines that cause myocarditisespecially in young men, although cases were usually relatively mild and people recovered quickly.

This is a very rare side effect vaccine attracted a lot of media attention and caused a lot of concern. This was one of the reasons why the UK did not routinely vaccinate young children until April 2022.

The latest findings support earlier studies suggesting that despite this rare side effect, vaccinated children had a lower risk of developing myocarditis than unvaccinated children. It's because most children have become infected with this virusand were therefore at higher risk of infection.

“I want to emphasize that these serious complications are really rare in children and young people in general,” says Angela Wood in the Cambridge HDR UK regional network, UK. “But we see that the risk was generally higher after Covid-19 infection than after vaccination.”

Wood's team analyzed National Health Service (NHS) data in England on almost 14 million children under 18 years of age between January 2020 and December 2021. In the second half of this period, 3.9 million children were vaccinated with the Pfizer/BioNTech vaccine, and 3.4 million were newly diagnosed with Covid-19 infection. The team couldn't look at later periods because not enough testing had been done.

This approach has limitations. For example, available data does not show whether children with these complications have fully recovered, and many milder cases of Covid-19 among children would not have been formally diagnosed. “However, despite these limitations, the scale of the data and the comprehensive linkage between all NHS data gives us quite a lot of confidence in our findings today,” says Wood.

“The caveat is that what applied during the strain of Covid-19 circulating at the height of the pandemic may not apply to the current strain of the virus,” he says. William Whiteley from the University of Edinburgh, UK, who was not involved in the study. His team reported last year that Covid-19 vaccines reduce the risk of heart attacks and strokes for at least six months after vaccination.

The fact that almost everyone except very young children now has some immunity to Covid-19 also means that the response to both additional vaccinations and reinfection with the virus will be different, a team member says. Pia Hardelid at University College London. “We need to continue this research,” she says.