Male adolescents and young adults have the highest risk for myocarditis after mRNA COVID-19 vaccination, with an increased risk for Moderna vaccines, according to an updated review published in The BMJ. Jennifer Pillay and colleagues conducted a living evidence synthesis and review to examine the incidence rates and risk factors for myocarditis and pericarditis after mRNA vaccination against COVID-19. Data were included from 46 studies. Male adolescents and male young adults had the highest incidence of myocarditis after mRNA vaccines (age 12-17: range, 50-139 cases per million; 18-29: range, 28-147 cases per million). The incidence of myocarditis after vaccination with BNT162b2 could be fewer than 20 cases per million among girls and boys aged 5-11 and women aged 18-29. Very low-certainty evidence was seen for incidence after a third dose of an mRNA vaccine.