Most COVID-19 vaccine recipients are well-versed in the common side effects that follow shots one and two in the Pfizer and Moderna series — a sore arm, maybe a headache, perhaps some muscle pain or fatigue. But a much rarer reaction has been drumming up concern lately: myocarditis, or inflammation of the heart muscle.
Here’s what you need to know about the condition and its link to COVID-19 and the vaccines.
1. Myocarditis has many causes
It may be the first time you’re seeing it in headlines, but myocarditis is not a new ailment. A number of things can cause it, including viral infections, certain medications, some autoimmune diseases, and exposure to environmental toxins like heavy metals and radiation. A reaction to a vaccine can also lead to myocarditis, although it’s rare, according to the National Heart, Lung and Blood Institute.
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.)
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One reason: You’re more likely to get myocarditis from COVID-19 than you are from the vaccine, research shows, and damage to the heart from the infection can be more severe. “Really, when we see severe myocarditis, or this severe inflammatory response in the heart, we're seeing it with actual acute COVID infection,” Gilotra says.
Another: COVID-19 can cause a long list of other serious complications beyond myocarditis, including damage to the brain and lungs — especially in older adults and in people with underlying health conditions, including heart disease, which is why people with existing heart problems shouldn’t be dissuaded from getting the vaccine.
“I've been advising my patients broadly — those with heart disease and even those without who are older — to get the COVID vaccine. I am not concerned about myocarditis,” Patel says.
Even younger people who are less likely to get severely ill from a coronavirus infection face risks with COVID-19, including multisystem inflammatory syndrome, or MIS-C — a condition that is “far more severe than the mostly self-resolving cases of vaccine-related myocarditis,” Gilotra says. There’s also the concern of long COVID, the term used to describe the lingering symptoms of illness that millions of COVID survivors have reported after a coronavirus infection.
Research shows that among the group of teens that experienced the highest rate of myocarditis after vaccination (about 63 cases per million doses of the second shot administered), the vaccines prevented an estimated 5,700 cases of COVID-19, as well as 215 hospitalizations and two deaths. What’s more, those that have been diagnosed with myocarditis after vaccination “have not experienced any long-term effects that we've been able to measure at this point,” says Yvonne Maldonado, M.D., an infectious disease expert and professor of pediatrics, epidemiology and population health at Stanford Medicine.
“The benefits really outweigh the risks related to vaccination,” Gilotra says. “And the reassuring thing is that so much of the 65-plus population has been vaccinated, so we have a lot of compelling data in this age group about the safety and the impact of vaccination in the pandemic.”
And remember: If you have questions, ask a trusted health care provider. “They can talk to you about your individual risk and any concerns and hesitancies you might have,” Gilotra says.
Symptoms of Myocarditis
Not everyone who has myocarditis develops symptoms, but those who do may experience:
- Chest pain
- Shortness of breath
- Feelings of having a fast-beating, fluttering or pounding heart
If you or your child/grandchild have any of these symptoms, seek medical care immediately, especially if it’s within a week after COVID-19 vaccination. Treatment may include pain medication, anti-inflammatories and several weeks of rest.
Rachel Nania writes about health care and health policy for AARP. Previously she was a reporter and editor for WTOP Radio in Washington, D.C. A recipient of a Gracie Award and a regional Edward R. Murrow Award, she also participated in a dementia fellowship with the National Press Foundation.