Debra L. Beck, MSc, and Eugene Braunwald, MD

On December 20, 2020, a national vaccination campaign against Covid-19 was started in Israel based on a two-dose regimen of the BNT162b2 messenger RNA vaccine (Pfizer-BioNTech). By May 31, 2021, approximately 5.12 million Israelis had been fully immunized against Covid-19. Mevorach and colleagues retrospectively reviewed data for this time period on all cases of myocarditis.  

A total of 304 cases of myocarditis (as defined by ICD-9 codes) were reported to the Ministry of Health. Of these, 196 were in persons who had received two doses of vaccine; the remaining 108 cases were in unvaccinated individuals.  

In 21 cases, an alternative diagnosis was ultimately made, while in the remaining 283 cases, 142 occurred after receipt of the BNT162b2 vaccine and 136 diagnoses were definitive or probable. Most cases occurred within the first few days after the second dose of vaccine.  

The clinical presentation was judged to be mild in 129 recipients (95%), with resolution seen in most cases; one fulminant case was fatal.  

The overall risk difference between the first and second doses was 1.76 per 100,000 persons (95% confidence interval [CI], 1.33 – 2.19), 3.19 (95% CI, 2.37 – 4.02) among male recipients and 0.39 (95% CI, 0.10 – 0.68) among women. The largest difference was seen in male recipients between the ages of 16 and 19 years (difference, 13.73 per 100,000 persons; 95% CI, 8.11 – 19.46).  

As compared with the expected incidence of myocarditis, the standardized incidence ratio was 5.34 (95% CI, 4.48 to 6.40) and was highest after the second dose in male recipients between the ages of 16 and 19 years (13.60; 95% CI, 9.30 to 19.20).  

The rate ratio 30 days after the second vaccine dose in fully vaccinated recipients, as compared with unvaccinated persons, was 2.35 (95% CI, 1.10 – 5.02); again, highest in male recipients between the ages of 16 and 19 years (8.96; 95% CI, 4.50 – 17.83), with a ratio of 1 in 6637 recipients. 

Summary 

The investigators concluded that the incidence of myocarditis, although low, was increased after the receipt of the BNT162b2 vaccine, particularly after the second dose among young male recipients. The clinical presentation of myocarditis after vaccination was usually mild. 

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