Aug. 26, 2021 -- Myocarditis, or inflammation of the heart muscle, appears to be more common after a COVID-19 infection than after vaccination, according to a new study published Wednesday in The New England Journal of Medicine.

Based in Israel, the study showed that Pfizer’s COVID-19 vaccine is linked to an increased risk of myocarditis, with about one to five cases per 100,000 people. But COVID-19 infection was linked to an increased risk of 11 cases per 100,000 people.

Coronavirus is very dangerous, and it’s very dangerous to the human body in many ways,” Ben Reis, PhD, one of the study authors and director of the Predictive Medicine Group at the Boston Children’s Hospital Computational Health Informatics Program, told The New York Times.

“If the reason that someone so far has been hesitating to get the vaccine is fear of this very rare and usually not very serious adverse event called myocarditis, well, this study shows that that very same adverse event is actually associated with a higher risk if you’re not vaccinated and you get infected,” he said.

Reis and colleagues analyzed electronic health records for nearly 2 million people from the largest health care organization in Israel. They calculated the rates of 25 harmful events that could be associated with COVID-19 vaccination or COVID-19 infection.

Overall, myocarditis was rare in both vaccinated and unvaccinated people. But it was more common in the vaccinated group, with about three extra cases for every 100,000 people.

Among those who had contracted COVID-19, there were 11 extra myocarditis cases for every 100,000 people, compared with those who had not been infected by the virus.

The study didn’t break down the risks for myocarditis by age or sex, though the median age of people who developed the heart problem after vaccination was 25. Among the 21 cases of myocarditis, 19 were men.

The Pfizer vaccine was also associated with an increased risk of swollen lymph nodes, appendicitis, and shingles. All three sides effects were uncommon.

COVID-19 infection was associated with higher risks of serious cardiovascular problems, including heart attacks, irregular heartbeat, blood clots in the lungs or legs, kidney injury, and bleeding in the skull. For every 100,000 infections, there were an extra 25 heart attacks and 62 cases of blood clots in the lungs.

“When you try to make your decision on whether or not you should take the vaccine, one of the things to ask is not only what are the potential adverse events associated with taking the vaccine, but also what am I risking when I think about COVID-19 as the other option,” Ran Balicer, MD, the lead study author and the chief innovation officer for Clalit Health Services in Israel, told the Times.

The FDA has been investigating the risks of myocarditis and pericarditis, or inflammation of the lining around the heart, in younger vaccine recipients, particularly adolescent and teen males.

Studies are ongoing, and the FDA said this week that Pfizer would do research on myocarditis and pericarditis risks in vaccinated people, including long-term effects on those who get sick, the newspaper reported.

Show Sources

The New England Journal of Medicine: “Safety of the BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Setting.”

The New York Times: “Heart Problem More Common After Covid-19 Than After Vaccination, Study Finds.”

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