Post-vaccine myocarditis, a condition marked by inflammation of the heart muscle, is a rare but potential complication following mRNA COVID vaccination.

It is estimated that approximately 18 cases of myocarditis occur per 1 million vaccine doses, making it a rare condition that can be challenging to study.

In a recent study, a team of researchers from Brigham and Women’s Hospital and Massachusetts General Hospital, founding members of Mass General Brigham, thoroughly examined the immunological response of 16 young adults and adolescents who developed myocarditis after receiving the COVID mRNA vaccine.

There were no changes in the amounts of antibodies, auto-antibodies, T cell profiles, or history of viral exposures, but the researchers did find higher levels of spike protein, cytokines (associated with innate inflammation), and troponin (indicating cardiac injury). Circulation reports their findings.

“The risk of developing severe disease from acute infection significantly outweighs this rare risk,” adds co-corresponding author Lael Yonker. “The incidence of myocarditis and other heart-related complications among children infected with SARS-CoV-2 is much higher than the risk of post-vaccination myocarditis.”

“Understanding the mechanisms that drive post-vaccine myocarditis could guide vaccine development in the future and give us important insights about the immune response,” adds co-corresponding author David Walt. “This was a precious sample set because these cases are so rare. We studied them in great depth, which led to an interesting finding that could guide treatment strategies to reverse post-vaccine myocarditis.”

Yonker, Walt, and their colleagues looked at blood samples from 61 teenagers and young adults. Of these, 16 got myocarditis and 45 didn’t have any problems after getting the Pfizer BNT162b2 or Moderna mRNA-1273 COVID-19 mRNA vaccines.

Specifically, they analyzed SARS-CoV-2-specific T cells, profiled cytokines and SARS-CoV-2 antigens, and tested for SARS-CoV-2-specific humoral responses and autoantibodies.

Both the antibody and the T cell responses were very identical in both the patients and controls. Using Simoa, a very sensitive test for finding single molecules, the group discovered that the blood of young teens with myocarditis had a lot more full-length Spike protein.

Adolescents in the control group who were asymptomatic and had received a vaccine did not have detectable levels of the Spike protein. The researchers also looked for the presence of anti-N IgG, a protein that indicates a recent SARS-CoV-2 infection. They did not find any, which suggests that natural infection was not a probable cause.

The study adds new information about post-vaccination myocarditis, but the authors say it is limited by a small sample size and can’t tell cause from effect. That is, it’s not clear whether the Spike protein itself causes inflammation in the heart muscle or is a biomarker of immune dysregulation that leads to myocarditis.

“In most cases, post-vaccination myocarditis is mild and self-resolving,” adds Yonker. “But new insights about its cause could further help us to improve patients’ symptoms or prevent this complication from occurring.”

Source: 10.1161/CIRCULATIONAHA.122.061025

Image Credit: John Smith/VIEWpress via Getty