Myocarditis risk after COVID vaccine low but higher in young men

A new study of 23.1 million Scandinavians suggests that the risk of myocarditis after vaccination with COVID-19 mRNA is low, but higher in men aged 16 to 24 years after the second dose. The results were published yesterday in the JAMA Cardiology🇧🇷

Researchers at the Norwegian Institute of Public Health studied the incidence of myocarditis (inflammation of the heart muscle) and pericarditis (swelling of tissues around the heart) among residents of Denmark, Finland, Norway and Sweden who were 12 years or older before vaccination or 28 years old. days after the first or second dose of the vaccine.

Eighty-one percent of participants were vaccinated at the end of the study. All were followed from December 27, 2020 to October 5, 2021.

Less than 30 cases per 100,000 vaccinated

Among all participants, 1077 and 1149 developed myocarditis and pericarditis, respectively, before or after vaccination.

One hundred and five participants developed myocarditis after the first dose of the Pfizer/BioNTech vaccine and 115 after the second. Among Moderna recipients, 15 developed myocarditis after the first dose, as did 60 after the second.

Of recipients of two doses of the same vaccine (homologous vaccination), the second dose was associated with a 75% elevated risk of myocarditis for Pfizer (adjusted incidence rate ratio [IRR], 1.75; 95% confidence interval [CI]1.43 to 2.14) and a risk more than six times greater for Moderna (IRR, 6.57; 95% CI, 4.64 to 9.28).

The researchers observed 9.7 cases of myocarditis per 100,000 person-years for unvaccinated males and 4.3 per 100,000 for females. Among all participants aged 16 to 24 years, myocarditis rates were 18.8 and 4.4 per 100,000 person-years for men and women, respectively.

The adjusted IRRs in vaccinated homologous men aged 16 to 24 years were 5.31 (95% CI, 3.68 to 7.68) after a second dose of Pfizer and 13.83 (95% CI, 8.08 to 23.68) for Modern. An estimated 5.55 (95% CI, 3.70 to 7.39) cases of excess myocarditis per 100,000 vaccinated occurred after the second dose of Pfizer, compared with 18.39 (95% CI, 9.05 to 27.72) after Modern. Pericarditis rates were similar.

The study authors concluded: “Our data are consistent with 4 to 7 excess events within 28 days per 100,000 vaccinated after a second dose of [Pfizer]and 9 to 28 excess events within 28 days per 100,000 vaccinated after a second dose of [Moderna]🇧🇷 The risk of myocarditis associated with SARS-CoV-2 vaccination must be weighed against the benefits of these vaccines.”

The benefits outweigh the low risk

In an essay, JAMA Cardiology Editor Ann Marie Navar, MD, PhD, University of Texas, and Associate Editor Robert Bonow, MD, Northwestern University, said the risk of COVID vaccine-related myocarditis is low and outweighed by the benefits of vaccination.

“At the individual level, immunization prevents not only COVID-19-related myocarditis, but also severe illness, hospitalization, long-term complications after COVID-19 infection, and death,” they wrote.

“At the population level, immunization helps slow community spread, lessens the chances of new variants emerging, protects immunocompromised people, and ensures how the health care system can continue to serve our communities.”

Myocarditis risk after COVID vaccine low but higher in young men

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