Long-Term Prognosis of Patients With Myocarditis

To the Editor Myocarditis, pericarditis, and myopericarditis are inflammatory heart conditions recognized as adverse events linked to COVID-19 mRNA vaccines, but their population-level clinical outcomes remain underdocumented. In a recent JAMA article, Ms Semenzato and colleagues provided valuable insights by comparing different myocarditis etiologies; the exclusion of pericarditis is notable. Accurate identification of myocarditis is crucial for both diagnosis and management. Case definitions from the Centers for Disease Control and Prevention and the Brighton Collaboration offer structured criteria, especially for vaccine-related cases. In the study by Semenzato and colleagues, myocarditis occurring within 7 days of vaccination was classified as postvaccine myocarditis, while myocarditis occurring within 30 days of SARS-CoV-2 infection was labeled post–COVID-19 myocarditis. In contrast, the Brighton Collaboration’s definitions, widely used in Canada for evaluating myocarditis and pericarditis after vaccination, include graduated levels of diagnostic certainty (definite, probable, possible) and consider events occurring within 6 weeks of vaccination as likely vaccine-associated. The Centers for Disease Control and Prevention reports onset of myocarditis symptoms ranging from 0 to 40 days after vaccination. while data from the Vaccine Adverse Event Reporting System, one of the largest global systems for tracking vaccine-associated adverse events, suggest that onset of myocarditis and pericarditis can extend beyond 120 days after vaccination. The study’s 7-day window may underestimate vaccine-associated myocarditis.