evidence: Two distinct self-limited syndromes, myocarditis and pericarditis, were observed after COVID-19 vaccination. Myocarditis developed rapidly in younger patients, mostly after the second vaccination. Pericarditis affected older patients later, after either the first or second dose. Some vaccines are associated with myocarditis,5 including mRNA vaccines,1-4 and the Centers for Disease Control and Prevention recently reported a possible association between COVID-19 mRNA vaccines and myocarditis, primarily in younger male individuals within a few days after the second vaccination, at an incidence of about 4.8 cases per 1 million.6 This study shows a similar pattern, although at higher incidence, suggesting vaccine adverse event underreporting. Additionally, pericarditis may be more common than myocarditis among older patients.