Myocarditis with COVID-19 mRNA Vaccines

Circulation. 2021 Jul 20. doi: 10.1161/CIRCULATIONAHA.121.056135. Online ahead of print.

Abstract

Myocarditis has been recognized as a rare complication of coronavirus 2019 (COVID-19) mRNA vaccinations, especially in young adult and adolescent males. According to the U.S. Centers for Disease Control (CDC), myocarditis/pericarditis rates are approximately 12.6 cases per million doses of second dose mRNA vaccine among 12-39-year-olds. In reported cases, patients with myocarditis invariably presented with chest pain, usually 2-3 days after a second dose of mRNA vaccination and had elevated cardiac troponin levels. ECG was abnormal with ST elevations in most, and cardiac MRI was suggestive of myocarditis in all tested patients. There was no evidence of acute COVID-19 or other viral infections. In one case, a cardiomyopathy gene panel was negative, but autoantibody levels against certain self-antigens and frequency of natural killer cells were increased. Although the mechanisms for development of myocarditis are not clear, molecular mimicry between the spike protein of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and self-antigens, trigger of preexisting dysregulated immune pathways in certain individuals, immune response to mRNA and activation of immunological pathways, and dysregulated cytokine expression have been proposed. The reasons for male predominance in myocarditis cases are unknown, but possible explanations relate to sex hormone differences in immune response and myocarditis, and also under-diagnosis of cardiac disease in women. Almost all patients had resolution of symptoms and signs, and improvement in diagnostic markers and imaging with or without treatment. Despite rare cases of myocarditis, the benefit-risk assessment for COVID-19 vaccination shows a favorable balance for all age and sex groups; therefore COVID-19 vaccination is recommended for everyone 12 years of age and older.