COVID Paper Database
Risk of Myocarditis after Pfizer Vaccination
Myocarditis after BNT162b2 mRNA Vaccine against Covid-19 in Israel
Reviewed by Charles Li
Visual Abstract
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Key Points
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Israel collected nationwide data on myocarditis after reports of vaccine-related cases of myocarditis.
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Based on these data, researchers determined that young men had a low but elevated risk of myocarditis.
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This risk was significantly higher after the second vaccine dose, compared to the first vaccine dose.
Background
Israel has vaccinated 5.1 million people with two doses of the Pfizer vaccine.
After receiving some reports of people developing myocarditis, a potential side effect of the vaccine, the Ministry of Health began actively monitoring for cases of myocarditis. They asked hospitals to report all cases of myocarditis.
In this study, researchers analyze and characterize the data to see who is at risk and how significant myocarditis risk is after COVID-19 vaccination.
Study Quote
After early reports of myocarditis during adverse events monitoring, the Israeli Ministry of Health initiated active surveillance.
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Study Design
Researchers studied cases of myocarditis in Israel reported between December 20, 2020, to May 31, 2021.
They compared observed rates of myocarditis after vaccination with standard expected rates of myocarditis. This comparison allowed them to potentially detect whether there were more cases of myocarditis in people who had just received the Pfizer vaccine.
If there were more cases of myocarditis after vaccination, it would suggest a link between vaccination and myocarditis risk.
This study found 283 total cases of myocarditis and 142 cases reported after receiving the Pfizer vaccine.
Study Quote
Among 304 persons with symptoms of myocarditis, 21 had received an alternative diagnosis. Of the remaining 283 cases, 142 occurred after receipt of the BNT162b2 vaccine; of these cases, 136 diagnoses were definitive or probable...
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Results
Overall, individuals were around twice as likely to develop myocarditis after their second dose compared to unvaccinated individuals.
This risk was highest in teenage boys between the ages of 16 and 19. In this age group, 1 in 6,637 developed myocarditis within 21 days of their second vaccine dose.
Researchers found that the risk of myocarditis increased dramatically between the first and second dose:
The risk of developing myocarditis was significantly higher after the second dose of the COVID-19 vaccine compared to the first dose. 3.83 out of every 100,000 men developed myocarditis after the second dose, compared to 0.64 after the first dose. This difference corresponded to a 3.19 (95CI = 2.37-4.02) risk difference.
Less than 1 in 100,000 men developed myocarditis after their first dose. Nearly 4 in 100,000 developed myocarditis after their second dose.
Myocarditis risk varied greatly in men based on their age. Teenagers between ages 16-19 had the highest risk of myocarditis.
Additionally, the risk of myocarditis varied significantly by age and gender. Men were far more likely to get myocarditis than women. Among men, risk varied significantly by age. As men got older, their risk dropped. The highest risk was in the youngest group studied: teenagers between ages 16-19.
Study Quote
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 to 5.02); the rate ratio was again highest in male recipients between the ages of 16 and 19 years (8.96; 95% CI, 4.50 to 17.83), with a ratio of 1 in 6637....
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Conclusion
Researchers in this study collected data from the entire country of Israel to estimate myocarditis risk after receiving the Pfizer vaccine.
By collecting data from an entire country, this study minimized the risk of sampling bias.
They determined that risk was highest in young men between ages 16-19. In most cases, they found that individuals developed their symptoms within days of receiving their second vaccine dose
They concluded that the risk of myocarditis after vaccination is low. But, it is higher in vaccinated individuals than unvaccinated individuals.
Study Quote
The incidence of myocarditis, although low, 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.
Visual Abstract: COVID-19 Vaccination & Myocarditis. Israel collected data on cases of myocarditis during their vaccination campaign. They found that the second dose carried a higher risk of myocarditis than the first. Young men ages 16-19 had the highest risk of myocarditis. Risk declined significantly with older age.