May 25, 2022

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What to Know About Myocarditis and COVID-19 Vaccines

The Centers for Disease Control and Prevention (CDC) says it is “actively monitoring” reports of myocarditis and pericarditis (inflammation of the sac that surrounds the heart) in a small share of people who have received the mRNA vaccines from Pfizer and Moderna; in most cases the condition occurs after the second shot. The agency estimates there are 12.6 cases of myocarditis per million second doses of mRNA COVID-19 vaccines administered to individuals 12 to 39 years of age. A more recent study published in JAMA Internal Medicine found a rate of 5.8 cases of myocarditis per million second doses in adults.

“The other thing that’s notable is that the vast majority of cases are self-resolving,” says Nisha Gilotra, M.D., an assistant professor of medicine and director of the Cardiac Sarcoidosis Program at Johns Hopkins Medicine — meaning most patients get better quickly after rest and without major medical treatment.

“In fact, [myocarditis] is probably underreported because so many of the cases can be asymptomatic or subclinical. A very rare proportion will [have symptoms that bring them into a health care setting] or be on the more severe spectrum,” Gilotra adds.

2. Vaccine-related myocarditis is uncommon — especially in older adults

It’s understandable for older adults to be concerned about anything heart-related, considering that heart disease is the leading cause of death and that adults 65 and older are more likely to suffer from it, says Manesh Patel, M.D., chief of cardiology at Duke University School of Medicine. But when it comes to vaccine-related myocarditis, the older population is largely unaffected.

The majority of the vaccine-related cases have been reported in male adolescents and younger adults. A CDC report published in June found that the rate of myocarditis was 40.6 cases per million second doses of mRNA COVID-19 vaccines administered for males 12 to 29 years of age, and 2.4 per million second doses administered to males 30 and older; rates for females in these age groups were 4.2 and 1 per million second doses, respectively.

The highest rates have been reported in males ages 12 to 17. This group saw about 63 cases of myocarditis per million second doses of mRNA COVID-19 vaccine administered.

This data reflects what the National Heart, Lung and Blood Institute says is true for most instances of myocarditis: It occurs more often in young adults. And the explanation likely boils down to immune response. In both myocarditis and pericarditis, the body’s immune system causes the inflammation when triggered by an infection or some other factor, the CDC says. And younger people tend to have more robust immune responses than their gray-haired peers.

“That’s why younger people seem to be more resistant to getting as sick with COVID than older people who don’t have this robust immune system,” Patel says. “It’s also maybe why you have younger people having a little bit more myocarditis than older people.”

3. COVID is more likely to cause myocarditis than vaccine

Still, top health experts, physicians, pharmacists and nurses groups across the country recommend that Americans 12 and up get the vaccine, noting that the benefits outweigh the small risk. (The vaccines are still being studied in kids under 12.)