Transient Myopericarditis Following Vaccination for COVID-19.

Clinical trials of the messenger ribonucleic acid (mRNA)-1273 vaccine developed by Moderna proved excellent safety and efficacy for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) prevention. However, the Centers for Disease Control and Prevention (CDC) has been investigating cases of myocarditis and pericarditis reported in the Vaccine Adverse Event Reporting System (VAERS) database. Currently, the CDC is reporting rates of 40.6 cases per million after second doses of mRNA vaccines administered to males 30 years or younger. Notably, the initial vaccine trials consisted of a limited number of adolescents and young adults; therefore, they were likely not powered to detect this rare potential side effect. We present a case of transient myopericarditis occurring in a young and healthy patient within 48 h of his second vaccination dose. Although a definitive causal relationship has yet to be determined, we came to this correlation because of the temporal association seen in our patient, secondary to the second dose of vaccination. Furthermore, we also suspect an autoimmune mechanism as the cause of cardiac injury, augmented by the increased vaccine reactogenicity seen in younger patients.