A bout with COVID-19 is more likely to cause myocarditis, or heart inflammation, than Pfizer's vaccine, according to a real-world study published Aug. 25 in the New England Journal of Medicine.
The research was based on EHR data from the largest healthcare organization in Israel. More than 880,000 people ages 16 and older who were fully vaccinated with Pfizer's shot as of May 24, as well as a matched control of unvaccinated individuals with the same number of people were included.
A total of 21 people in the vaccinated group developed myocarditis, most of whom were men with a median age of 25.
Scientists did find a link between the vaccine and an increased risk for myocarditis; an extra 2.7 cases of myocarditis per 100,000 vaccinated people, compared to the unvaccinated group. However, the risk was much higher among people who contracted COVID-19 at 11 cases per 100,000, compared to those who hadn't been infected, the findings showed.
"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," Ben Reis, PhD, study co-author and director of the predictive medicine group at Boston Children's Hospital's computational health informatics program, told The New York Times.
A COVID-19 infection was also tied to higher risk for other heart problems, including heart attacks, irregular heartbeat and blood clots. Meanwhile, Pfizer's vaccine was associated with an increased risk of swollen lymph nodes, appendicitis and shingles.
Pfizer's COVID-19 shot was the first in the U.S. to receive full FDA approval Aug. 23. The agency has said the shot is associated with an increased risk of myocarditis and pericarditis and is requiring the drugmaker to conduct postmarket studies to further assess the risks. In an analysis from this week, which was based on data from unconfirmed reports, the FDA estimated the risk of the conditions in vaccinated boys ages 16-17 may be as high as 1 in 5,000. However, even in the worst-case scenarios, benefits of the vaccine still outweigh the risks, the analysis concluded.