Administration of BNT162b2 mRNA Vaccine against Covid-19 and Myocarditis in Israel

A passive surveillance program was started at the start of the immunization campaign to track any adverse events that occurred 21 days after the first dose of vaccine and 30 days after the second dose. As required by Israeli legislation, health care providers reported these data to the Ministry of Health. Following reports of myocarditis, the Ministry of Health began active surveillance in February 2021, requiring all hospitals to report all cases of myocarditis, including those diagnosed since December 2020, with or without pericardial effusion, and regardless of vaccination status.

By May 31, 2021, about 5.1 million Israelis had received two doses of the BNT162b2 messenger RNA vaccine (Pfizer–BioNTech) and were fully vaccinated against coronavirus disease 2019 (Covid-19). The Israeli Ministry of Health began rigorous surveillance after early reports of myocarditis during adverse event monitoring.

136 cases of definite or probable myocarditis were recorded in temporal proximity to the receipt of two doses of the BNT162b2 mRNA vaccine during a nationwide vaccination campaign that took place from December 2020 to May 2021, involving more than 5 million residents — a risk that was more than twice that of unvaccinated people. Within the first week after the second treatment, this connection was strongest in young male recipients.

Within 21 days of receiving the second vaccine dosage, definite or probable cases of myocarditis occurred in about 1 of 6637 male recipients and 1 of 99,853 female recipients, according to research.

The authors analyzed data on all cases of myocarditis collected between December 20, 2020, and May 31, 2021, and classified the information using the Brighton Collaboration definition. They calculated the risk difference for comparing the incidence after the first and second vaccine doses (21 days apart); the standardized incidence ratio of the observed-to-expected incidence within 21 days after the first dose and 30 days after the second dose, independent of certainty of diagnosis; and the rate ratio for comparing the incidence after the first and second vaccine doses (21 days apart).

21 of the 304 people who experienced myocarditis symptoms had been given a different diagnosis. 142 of the remaining 283 instances occurred after receiving the BNT162b2 vaccine; 136 diagnoses were definitive or probable in these cases. In 129 (95 percent) of the patients, the clinical presentation was modest; one fulminant case was fatal. The total risk difference between the first and second doses was 1.76 per 100,000 people (95 percent confidence interval [CI], 1.33 to 2.19), with the highest change occurring among male recipients aged 16 to 19. (difference, 13.73 per 100,000 persons; 95 percent CI, 8.11 to 19.46).

The standardized incidence ratio was 5.34 (95 percent CI, 4.48 to 6.40) and was highest after the second dosage in male receivers between the ages of 16 and 19 years, compared to the expected incidence based on historical data (13.60; 95 percent CI, 9.30 to 19.20). The rate ratio was 2.35 (95 percent CI, 1.10 to 5.02) 30 days after the second vaccine dose in fully vaccinated recipients compared to unvaccinated people; the rate ratio was highest in male recipients between the ages of 16 and 19 years (8.96; 95 percent CI, 4.50 to 17.83), with a ratio of 1 in 6637.

Although the frequency of myocarditis was modest, it rose after receiving the BNT162b2 vaccination, especially among young male patients after the second dose. Myocarditis after vaccination usually had a modest clinical manifestation.