Low rate of myocarditis seen after COVID-19 vaccination

Following the approval of the COVID-19 BNT162b2 vaccine (Pfizer-BioNTech) in Israel, surveillance was initiated to monitor adverse events, ultimately resulting in reports of myocarditis after vaccination.

Thus, the present study presented both clinical and epidemiological features and follow-up results of myocarditis cases diagnosed in temporal proximity to vaccination, in order to examine the potential for a causal relationship between the COVID-19 vaccine and myocarditis.

A team of investigators, led by Dror Mevorach, MD, Hadassah Hebrew University Medical Center, observed that the incidence of myocarditis, although considered low, increased after receiving the COVID-19 vaccination, especially after the second dose in young male recipients.


A retrospective review of data on suspected cases of myocarditis was performed, with medical records obtained from the database of the Ministry of Health in Israel. Data was obtained from December 2020 to May 2021.

The myocarditis criteria were adapted using the Bright Collaboration case definition and classified as definitive, possibly possible, with insufficient data or with another diagnosis.

Investigators used descriptive frequencies, percentages, means, and standard deviations to characterize cases of myocarditis based on age, sex, time since vaccination, length of hospital stay, and clinical results.

In addition, the investigators analyzed the occurrence of myocarditis by calculating the risk difference for the comparison of the incidence of myocarditis after the first and second doses of vaccine, 21 days apart.

Then, they calculated the standardized incidence ratio of observed incidence to expected incidence within 21 days after the first dose and 30 days after the second dose. In addition, they calculated the ratio of rates 30 days after the second dose, compared to unvaccinated patients.


In Israel, a total of 9,289,765 were included in the surveillance period, of which 5,125,635 received 2 doses. Data shows that 304 people had symptoms of myocarditis reported to the Israeli Ministry of Health.

After excluding 21 cases due to an alternative diagnosis, a total of 283 cases confirmed the diagnosis of myocarditis. Of these cases, 142 cases occurred after vaccination, 136 of these diagnoses being certain or probably myocarditis.

In addition, the clinical presentation was considered benign in 129 people who received the vaccine, while one person with fulminant myocarditis died.

Data show that the overall risk difference between the first and second dose was 1.76 per 100,000 people (95% confidence interval, 1.33 – 2.19), showing an overall risk difference of 3 , 19 (95% CI, 2.37 – 4.02) in men and 0.39 (95% CI, 0.10 – 0.68) in women.

They found that the greatest difference was in male patients aged 16-19, with a difference of 13.73 (95% CI, 8.11 – 19.46).

In addition, the standardized incidence ratio of myocarditis after the second vaccine dose was 5.34 (95% CI, 4.48 – 6.40). In men, the standardized incidence ratio was highest in 16-19 year olds at 13.60 (95% CI 9.30-19.20).

Investigators observed that fully vaccinated recipients, compared to unvaccinated patients, had a rate ratio 30 days after the second vaccine dose of 2.35 (95% CI, 1.10 – 5.02). It was found to be highest in men aged 16 to 19 at 8.96 (95% CI, 4.50 to 17.83).

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Investigators noted that the incidence of myocarditis decreased as the number of newly vaccinated people decreased over time, suggesting the possibility of a causal relationship between myocarditis and vaccination.

“The mechanism of vaccine-induced myocarditis is not known but may be related to the active component of the vaccine, the mRNA sequence that encodes the spike protein of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV- 2), or the immune response following vaccination, ”the investigators wrote.

The study, “Myocarditis after BNT162b2 mRNA Vaccine against Covid-19 in Israel”, was published in the New England Journal of Medicine.

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