evidence: Data sources Medline, Embase and the Cochrane Library were searched from October 2020 to January 10, 2022; reference lists and grey literature (to January 13, 2021). [...] Case reports and surveillance signals of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the two-layered sac surrounding the heart) after COVID-19 vaccination appeared as early as April 2021. [...] Question 1: Incidence of Myocarditis and Pericarditis Following COVID-19 Vaccination