Covid raises risk of heart issues in children more than vaccination

The evidence that children are better off being vaccinated against covid-19 rather than infected during the pandemic has become even stronger. The largest study ever, involving almost 14 million children, found that the risk of serious – but very rare – side effects involving the heart and blood vessels was much higher after an infection than after a vaccination.

For example, among children ages 5 to 18, 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 to other periods. Among those who received the Pfizer/BioNTech mRNA vaccine for the first time, there were almost 2 fewer cases per 100,000.

In cases of inflammation of the heart muscles, known as myocarditis, there were more than 2 additional cases per 100,000 within six months of infection. Among those vaccinated, there was less than one additional case. In other words, the risk of myocarditis was more than twice as high after infection as after vaccination.

Reports of covid-19 infections causing myocarditis were published as early as April 2020. After vaccinations began in December of that year, reports also began to emerge of vaccines triggering myocarditis, particularly in young men, although cases are usually relatively mild and people recover quickly.

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

The latest findings confirm previous studies suggesting that despite this rare side effect, vaccinated children had a lower risk of myocarditis than those who were not vaccinated. This is because most children have been infected with the virus and have therefore been exposed to a higher risk of infection.

“I would like to emphasize that these serious complications are very rare in children and young people in general,” says Angela Wood of the Cambridge HDR UK Regional Network, United Kingdom. “But we see that the risk was generally higher after a covid-19 infection than after a vaccination.”

Wood’s team analyzed data from almost 14 million children aged under 18 in England’s National Health Service (NHS) for the period January 2020 to December 2021. During the second half of this period, 3.9 million children were vaccinated with the Pfizer/BioNTech vaccine and 3.4 million were diagnosed with covid-19 infection for the first time. The team couldn’t look at later periods because there wasn’t enough testing done.

The approach has limitations. For example, available data does not reveal whether children with these complications have fully recovered, and many milder cases of covid-19 in children would not have been officially diagnosed. “However, despite these limitations, the scale of the data and the comprehensive linkage of all NHS data gives us great confidence in our overall findings today,” says Wood.

“The condition is that what applied to the covid-19 strain circulating at the height of the pandemic might not apply to the current strain of the virus,” says William Whiteley of the University of Edinburgh, UK, who was not involved in the study. His team reported last year that covid-19 vaccines reduced the risk of heart attack and stroke 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 additional booster shots and reinfections with the virus will be different, says team member Pia Hardelid from University College London. “We need to continue doing these studies,” she said.