The Israel Health Ministry announced on Tuesday that it had detected a link between Pfizer’s COVID vaccine and a type of heart inflammation called myocarditis. The link only appears to hold in young men — but even then, there are very few cases, and it has by no means been definitively determined that the vaccine is causing the condition.
So what exactly did they find?
Israeli researchers studied more than 5 million people that had been vaccinated against COVID-19 and found 275 cases of myocarditis between December 2020 and May 2021. This is within expected background rates for the condition. However, more myocarditis cases than would have been expected were reported in young men aged 16 to 30 who received the Pfizer vaccine.
It’s crucial to look into “even a hint of a signal,” Douglas Diekema, a pediatrician, and bioethicist at Seattle Children’s Hospital, told Science. However, “while this report is suggestive… it requires validation in other populations by other investigators before we can be certain the link exists.”
Young men are generally at higher risk for myocarditis, but the prevalence found in this study was 5 to 25 times higher than expected in young vaccinated guys. It was most common in those aged 16 to 19.
Still, the overall risk was low. The researchers concluded that only between one in 3,000 and one in 6,000 men aged 16 to 24 developed the condition. Ninety-five percent of the cases were mild, and most people spent four days or less in the hospital. Myocarditis typically only requires treatment with anti-inflammatory drugs.
One concern is that myocarditis could show up in children aged 12 to 15 now that they have started to receive the vaccine. But experts don’t expect the possible link to affect vaccination guidelines for children.
“I can’t imagine it’s going to be anything that would cause medical people to say we shouldn’t vaccinate kids,” Diekema said. “I don’t know many physicians who are changing their minds about vaccinating their kids.”
The potential link isn’t limited to Pfizer. The U.S. has also been investigating whether myocarditis in young people is related to the Moderna vaccine, which like Pfizer is an mRNA vaccine. In late May, a Centers for Disease Control and Prevention advisory group found a higher number than expected cases of myocarditis and pericarditis, another type of heart inflammation, in young vaccinated people aged 16 to 24. However, other data did not support this association. The CDC advisory group recommended further inquiry into the subject.
In any case, the risk of forgoing vaccination and getting COVID-19 is greater than the risk of getting vaccinated and developing myocarditis. This is true even for children, who relatively have a low risk of severe COVID-19. So experts still recommend getting vaccinated.
“This issue of a transient myocarditis associated with a vaccine is at the moment a theoretical and unproven risk,” Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, told Reuters. “So I think that in the world of trying to weigh relative risks, the disease is a greater risk.”