Myocarditis or Pericarditis Following mRNA COVID-19 Vaccination

colleagues 1 describe findings from a population-based cohort study in Ontario, Canada, that used data from a passive vaccine-safety surveillance system to evaluate reported rates of myocarditis or pericarditis following receipt of an mRNA COVID-19 vaccine, mRNA-1273 (Moderna Spikevax) or BNT162b2 (Pfizer-BioNTech Comirnaty). The authors found that reported rates of myocarditis or pericarditis were higher after vaccination with mRNA-1273 compared with BNT162b2 and that for both vaccines, the rate was higher following dose 2 of the primary 2-dose series when the interdose interval (the timing between dose 1 and dose 2) was 30 days or less. These findings add to the body of knowledge about the association of mRNA COVID-19 vaccination with myocarditis and pericarditis and offer additional insight into the differential risk between the 2 mRNA COVID-19 vaccine products and the possible association of the interdose interval with risk of myocarditis or pericarditis.