How often do vaccines cause heart issues in kids?

Federal regulators are reviewing data on the link between Moderna’s coronavirus vaccine and a rare heart problem in adolescents, the company announced last week. That side effect — myocarditis, an inflammation of the heart muscle — has also worried advisers to federal agencies regarding use of the Pfizer-BioNTech vaccine in younger children and teenagers.

So how common is myocarditis, really? And should parents be concerned about vaccinating their children?

Absolutely not, said several experts familiar with the recent studies. While the vaccines made by Pfizer-BioNTech and Moderna do seem to be associated with an increased risk of myocarditis, the absolute risk remains very small. Most cases are mild and resolve quickly.

“If you look at an isolated risk, you could really get yourself very worked up and scared,” said Dr. Brian Feingold, an expert on heart inflammation in children at UPMC Children’s Hospital of Pittsburgh.

But COVID-19 itself, he noted, is much more apt to damage the heart permanently: “Statistically, that’s way more likely.”

Myocarditis generally results from infection with a virus or bacteria, and causes symptoms like rapid or irregular heartbeat, chest pain and shortness of breath. Globally, about 10 to 20 people out of every 100,000 develop myocarditis each year, but many others have mild symptoms and may never be diagnosed.

Since the start of the coronavirus pandemic, tens of thousands of children have been hospitalized with COVID, and 657 have died, according to data collected by the CDC.

Some children who are infected with the coronavirus may go on to develop long COVID, remaining ill for months after the initial infection is gone, or multisystem inflammatory syndrome, which has affected at least 5,200 children in the U.S.

While the risk of myocarditis after vaccination is real, “those are real numbers that are bigger,” Feingold said.

The incidence of myocarditis after vaccination varies with age, sex and dose — and across studies. But the trend so far suggests that the chances are highest after the second dose of an mRNA vaccine in male patients ages 16 to 29.

There are roughly 11 cases of myocarditis for every 100,000 vaccinated male patients in this age group, one study estimated. The odds of myocarditis decrease with age.

Data on adolescents ages 12 to 15 is limited, because the Pfizer-BioNTech vaccine only recently became available to them. But so far, heart problems after vaccination seem to be less common in boys of that age than in older men, said Dr. Paul A. Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia.

This age distribution is similar to that seen among patients with myocarditis caused by viral infections, Offit said.

An FDA scientific advisory committee, on which he sits, met recently to review the Pfizer-BioNTech vaccine’s safety in children ages 5 to 11 and ultimately voted to recommend that children be given the vaccine.

“Myocarditis is usually a post-pubertal phenomenon,” Offit said, adding, “That made me feel better about the fact that we won’t be unpleasantly surprised” by a surge in myocarditis in younger children after they are immunized.

That reassurance may not be enough for some parents. Jeff Gustin, a plant geneticist at the Agriculture Department, said he and two of his sons had elevated heart rates after getting the Pfizer-BioNTech vaccine.

His teenage sons recovered quickly, but Gustin, 42, says he can still feel his heart beating hard, especially when he lies down. Now he is considering a booster of the Johnson & Johnson vaccine, rather than of the Pfizer-BioNTech or Moderna vaccine.