With the administration of the first COVID vaccines two years ago, public health officials found an increase in cases of myocarditis, particularly among young males who had been vaccinated with mRNA vaccines. The underlying cause of these reactions remained a mystery.
Now Yale scientists have identified the immune signature of these heart inflammation cases. Published in the journal Science Immunology, their findings eliminate some of the theorised causes of the heart inflammation and point to the consequences of a slightly over-stimulated immune system.
Myocarditis is a generally mild inflammation of heart tissue which can cause scarring but is usually resolved within days. The increased incidence of myocarditis during vaccination was seen primarily in males in their teens or early 20s, who had been vaccinated with mRNA vaccines, which are designed to elicit immune responses specifically to the SARS-CoV-2 virus.
According to the Centers for Disease Control and Prevention (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. The incidence of myocarditis was 50.1 to 64.9 cases per 100 000 after infection with the COVID virus among males in this age group.
For the new study, the Yale research team conducted a detailed analysis of immune system responses in those rare cases of myocarditis among vaccinated individuals. They found that the heart inflammation was not caused by antibodies created by the vaccine, but rather by a more generalised response involving immune cells and inflammation.
“The immune systems of these individuals get a little too revved up and over-produce cytokine and cellular responses,” said team leader Carrie Lucas, associate professor of immunobiology.
Earlier research had suggested that increasing the time between vaccination shots from four to eight weeks may reduce risk of developing myocarditis.
Lucas noted that, according to CDC findings, the risk of myocarditis is significantly greater in unvaccinated individuals who contract COVID than in the vaccinated. She emphasised that vaccination offers the best protection from COVID-related disease.
“I hope this new knowledge will enable further optimising 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 MD/PhD student at Yale School of Medicine, who is a co-first author of the paper with Jon Klein, also a Yale MD/PhD student.
Source: Yale University
