Epidemiological Characteristics and Outcome of Myocarditis and Pericarditis Temporally Associated With BNT162b2 COVID-19 Vaccine in Adolescents: Korean National Surveillance.

Background: This study aimed to investigate the epidemiological characteristics and outcomes of myocarditis/pericarditis after BNT162b2 vaccination in Korean adolescents.

Methods: This was a retrospective cohort analysis of adolescents aged 12-19 years old diagnosed with myocarditis/pericarditis within 42 days of BNT162b2 mRNA vaccination. All reported cases were investigated by city or government epidemiologists and the diagnostic certainty and causality was determined by the Korea Disease Control and Prevention Agency's Adverse Event Following Immunization Expert Advisory Committee according to the modified version of Brighton Collaboration Myocarditis/Pericarditis Working group's case definitions.

Results: A total 3,709,063 adolescents aged 12-19 received 8,135,240 doses of the BNT162b2 vaccine in South Korea, and 184 cases met the Brighton criteria for the case definition of myocarditis and pericarditis with diagnostic certainty of possible and above. The median age was 17 years old (interquartile range [IQR], 15-18) and boys accounted for 81.5% (n = 150/184) of the cases. The overall incidence was 2.25 (95% confidence interval [CI], 1.94-2.60) cases per 100,000 doses and severe cases was 0.25 (95% CI, 0.15-3.80) cases per 100,000 doses. The highest incidence rate was observed in boys after the second dose, with 5.01 (95% CI, 4.12-6.17) cases per 100,000 doses. A total 89.1% (164/184) were classified as mild, and no deaths were reported.

Conclusion: The highest incidence of myocarditis/pericarditis after BNT162b2 immunization was observed in male adolescents after the second dose, with majority of the cases presenting with a mild clinical course and favorable outcome.