Every medical intervention comes with both benefits and risks. For vaccinations, the benefits greatly outweigh any potential hazards in most people.
The new COVID-19 vaccines based on mRNA technology are no exception. But one risk associated with them—myocarditis, especially for young men—has raised concerns among the public.
A new study published in JAMA has found that the risk associated with getting myocarditis—which is inflammation of the heart muscle, often triggered by the immune system as it responds to an infection—shortly after getting the COVID-19 vaccine is lower than the risk that can come from getting the disease.
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Researchers led by Dr. Mahmoud Zureik, professor of epidemiology and public health at the University of Versailles, studied people ages 12 to 49 who had been hospitalized with myocarditis in France from Dec. 2020 to June 2022, when mass vaccination campaigns were taking place. They sorted people into three groups: people who developed myocarditis and were hospitalized within seven days of receiving an mRNA shot, those who were admitted to the hospital within 30 days of getting COVID-19 but had not had an mRNA vaccine in the prior seven days, or people who had myocarditis that was due to other causes. Everyone was followed for 18 months.
In that time period, people with vaccine-related myocarditis were half as likely to be readmitted to the hospital for myocarditis or heart-related events compared to those with infection-related myocarditis or people with myocarditis due to other causes.
The findings indicate that the risk of myocarditis linked to the mRNA vaccines “is very, very low,” says Zureik. And it’s important to remember that the risk of COVID-19 to the heart “is not limited to myocarditis. There are other cardiovascular risks as well.”
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The results are timely, as COVID-19 cases and emergency room visits continue to climb in the U.S.. The increases are due in part to new variants and waning immunity people have from their last vaccines, which targeted different versions of SARS-CoV-2. That’s why the U.S. Food and Drug Administration recently approved an updated version of the vaccine to recognize the currently circulating variants. But uptake of recent shots has been low.
The study did not delve into the reason why the vaccines are linked—however slightly—to myocarditis, or why the immune system’s response to the vaccine seems to be different than that generated by a COVID-19 infection. It’s possible that because people are aware of the potential myocarditis risk associated with the vaccine, people hospitalized for the condition after getting vaccinated could have milder cases, Zureik says.
More research is needed to better understand how the mRNA vaccines are interacting with the body’s immune system, but the findings provide some confidence that the shots do not seem to be associated with any substantially greater risk of heart inflammation, even months after immunization.
