Nov. 25, 2022 — Myocarditis after SARS-CoV-2 vaccination is rare but more common in younger men, especially after the second vaccine mRNA-1273 (Moderna), suggesting that it should to take into account the type of vaccine, age and gender when vaccinating. The study was published in CMAJ (Canadian Medical Association Journal)
“In this study, we found higher observed rates of myocarditis after receiving mRNA vaccines than expected, but the absolute rates were low,” wrote Dr. Naveed Janjua, School of Population and Public Health, University of British Columbia and Center for British Columbia Disease Control, Vancouver, British Columbia, with co-authors.
Researchers analyzed population health data from the BC COVID-19 cohort, which includes more than 10.2 million doses of mRNA vaccines administered to people aged 12 years and older from December 15, 2020 to March 10, 2022. Almost 7 million were BNT162b2 (Pfizer-BioNTech) doses and 3.2 million were mRNA-1273 (Moderna) doses. The researchers identified people who were admitted to the hospital or visited the emergency department for myocarditis within 7 and 21 days of receiving the vaccine.
The mean incidence of myocarditis 21 days after vaccination was 1.37 per 100,000 persons compared with an expected incidence of 0.39 per 100,000 unvaccinated persons. The highest rates of myocarditis were in men (incidence: 2.15/100,000), among those aged 18–29 years (incidence: 2.97/100 00), after the second dose (incidence: 2.27/100 000 doses) and in humans vaccinated with mRNA-1273 (Moderna) (rate: 1.75/100,000). Among men aged 18-29 who received the mRNA-1273 (Moderna) vaccine, the rate was 22.9/100,000 doses. After the third dose, the incidence of myocarditis was lower, including among people aged 18-29 years.
“The overall incidence of myocarditis per 100,000 doses was still very low for both vaccines,” the authors wrote. However, they state that their findings “… support the preferential use of the BNT162b2 vaccine (Pfizer-BioNTech) over the mRNA-1273 vaccine (Moderna) in people aged 18–29 years.”
A US analysis estimates that 11,000 cases of COVID-19, 560 hospitalizations, 138 ICU hospitalizations, and 6 deaths from COVID-19 could be prevented per million second doses of SARS-CoV-2 mRNA vaccine administered to men at age 12–29 years, compared with 39–47 expected cases of myocarditis after SARS-CoV-2 vaccination.
“[T]the benefits of SARS-CoV-2 vaccination in reducing the severity of COVID-19, hospital admissions, and deaths far outweigh the risk of developing myocarditis. … Thus, continued vaccination of this group, along with monitoring for adverse events, including myocarditis, should remain the preferred strategy,” the authors conclude.
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