Myocarditis After BNT162b2 Vaccine Receipt in Israel

Defining the frequency and severity of myocarditis after vaccination has great public health importance. Two retrospective Israeli studies have addressed this issue, one in a large healthcare organization and the other throughout the country, where there was a national campaign to administer BNT162b2 messenger RNA vaccine (Pfizer-BioNTech).

In a survey of Israel's largest healthcare organization, researchers identified 54 cases of myocarditis within 42 days of the first vaccine dose among 2.6 million partially or fully vaccinated members. The severity was mild in 41, intermediate in 12, and fulminant in 1. The median patient age was 27 years, and 94% were male. Eighty-three percent had no coexisting medical condition, and 69% were diagnosed after the second dose. The incidence was 2.1 cases per 100,000 overall, 4.1 per 100,000 for males, and 0.2 per 100,000 for females and was highest (10.7 per 100,000) among males aged 16 to 29 years. Overall, the risk of fulminant myocarditis was 0.04 per 100,000.

In the national study, investigators identified 304 cases among 9.3 million people. The cases occurred most frequently in the first few days after the second dose. The standardized incidence ratio (observed cases divided by expected cases) was 1.42 after the first dose and 5.34 after the second dose. The estimated incidence rate was about 4 per 100,000 in males and 0.5 per 100,000 in females after the second vaccine dose. Among the 136 cases of definite or probable myocarditis, 129 were mild. The ejection fraction was normal or mildly reduced in most people.