Myocarditis and Pericarditis Are Rare After mRNA COVID-19 Immunization

Reports of myocarditis and pericarditis after COVID-19 vaccination began to appear shortly after the start of widespread immunization in early 2021. Cases were rare (1–10 cases per 100,000 person-years) but occurred most frequently among young men who received mRNA vaccines.

Researchers conducted a systematic review of 46 large observational and surveillance studies (each with >10,000 patients) and case series. They reached these conclusions:

• Incidence of myocarditis after mRNA vaccines was greatest in male adolescents and young adults (between 30 and 150 cases per million) and probably was higher with the Moderna mRNA vaccine than with the Pfizer mRNA vaccine.

• In adolescents and young adults, incidence of myocarditis or pericarditis after the second dose of an mRNA vaccine might be lower when the interval between doses is >30 days; in men who were 18 to 29, the dose interval was at least 56 days to observe a decrease in postvaccine myocarditis or pericarditis.

• Male adolescents and young men with myocarditis typically noted onset of symptoms 2 to 4 days after the second dose and were hospitalized briefly (mean, 2–4 days).

• Three small case series suggested persistent electrocardiogram abnormalities and ongoing symptoms or need for drug treatment for as long as 3 months in more than half of patients.