Key points:
- Yale researchers have linked the increase in myocarditis with overactivation of immune cells.
- The team did not find any link to the COVID-19 mRNA vaccines.
- Data shows the risk of myocarditis is significantly greater in unvaccinated individuals who contract the COVID-19 virus than in those who receive vaccines.
When new COVID-19 vaccines were first administered two years ago, researchers, clinicians and public health officials saw an increase in cases of myocarditis, or inflammation of the heart muscle. It was particularly evidence among young males who had been vaccinated with mRNA vaccines. But, at the time, it was unclear what was causing the reaction.
A new study from Yale scientists shows that myocarditis was not caused by antibodies created by the vaccine, but rather by a more generalized response involving immune cells and inflammation. The findings suggest potential ways to further reduce the incidence of a still rare side effect of vaccination, the authors say.
According to the CDC, among males aged 12 to 17, about 22 to 36 per 100,000 experienced myocarditis within 21 days after receiving a second vaccine dose. Among unvaccinated males in this age group, the incidence of myocarditis was 50.1 to 64.9 cases per 100,000 after infection with the COVID-19 virus.
For the study, published in Science Immunology, the Yale research team conducted a detailed analysis of immune system responses in cases of myocarditis among vaccinated individuals.
“The immune systems of these individuals get a little too revved up and over-produce cytokine and cellular responses,” said study author Carrie Lucas, associate professor of immunobiology at Yale.
Lucas noted that, according to CDC findings, the risk of myocarditis is significantly greater in unvaccinated individuals who contract the COVID-19 virus than in those who receive vaccines.
“I hope this new knowledge will enable further optimizing mRNA vaccines, which, in addition to offering clear health benefits during the pandemic, have a tremendous potential to save lives across numerous future applications,” said Anis Barmada, an M.D./Ph.D. student at Yale School of Medicine, who is a co-first author of the paper.