“Importance: Increased rates of myocarditis or pericarditis following receipt of COVID-19 mRNA vaccines have been observed. However, few available data are associated with differences in rates of myocarditis or pericarditis specific to vaccine products, which may have important implications for vaccination programs…
Results: Among 19?740?741 doses of mRNA vaccines administered, there were 297 reports of myocarditis or pericarditis meeting the inclusion criteria; 228 (76.8%) occurred in male individuals, and the median age of individuals with a reported event was 24 years (range, 12-81 years). Of the reported cases, 207 (69.7%) occurred following the second dose of the COVID-19 mRNA vaccine. When restricted to individuals who received their second dose during the period of enhanced passive surveillance (on or after June 1, 2021), the highest rate of myocarditis or pericarditis was observed in male individuals aged 18 to 24 years following mRNA-1273 as the second dose (299.5 cases per 1,000,000 doses; 95% CI, 171.2-486.4 cases per 1,000,000 doses); the rate following BNT162b2 as the second dose was 59.2 cases per 1,000,000 doses (95% CI, 19.2-138.1 cases per 1,000,000 doses). Overall rates for both vaccine products were significantly higher when the interdose interval was 30 or fewer days (BNT162b2: 52.1 cases per 1,000,000 doses [95% CI, 31.8-80.5 cases per 1,000,000 doses]; mRNA-1273: 83.9 cases per 1,000,000 doses [95% CI, 47.0-138.4 cases per 1,000,000 doses]) compared with 56 or more days (BNT162b2: 9.6 cases per 1,000,000 doses [95% CI, 6.5-13.6 cases per 1,000,000 doses]; mRNA-1273: 16.2 cases per 1,000,000 doses [95% CI, 10.2-24.6 cases per 1,000,000 doses]).”
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