Vaccination is still recommended for everyone 12 and older.

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A vaccine safety panel on Wednesday cited a "likely association" between COVID-19 mRNA vaccination and a rare risk of heart issues in adolescents and young adults.

The update is based on a review of reports to the Vaccine Adverse Event Reporting System (VAERS), the nation's early warning system for vaccine safety, and other surveillance activities.

Cases of myocarditis (or inflammation of the heart) and pericarditis (inflammation of the tissue surrounding the heart) are occurring most often within a week after the second dose of the Pfizer and Moderna vaccines, and in males more than females, according to data presented at the meeting of the Advisory Committee on Immunization Practices (ACIP).

Scientists noted that these problems appear to be rare and mostly not serious.

As of June 21, VAERS has received more than 600 reports of myocarditis or pericarditis in people 30 and younger who received a COVID vaccine, mostly the mRNA vaccines, according to the US Centers for Disease Control and Prevention (CDC). Of those, the CDC and US Food and Drug Administration have confirmed 393 cases.

Tom Shimabukuro, MD, deputy director for the CDC's Immunization Safety Office, noted that the number of reports exceed the number of cases that would be expected to occur regardless of vaccination. However, early data for adolescents and young adults ages 12 to 39 suggests that these problems are occurring at a rate of 12.6 per million doses.

The CDC has identified 1,200 cases of heart problems among people of all ages after vaccination, per the New York Times.

CDC continues to recommend vaccination for everyone 12 and older to protect against COVID-19 and its potentially severe complications.

However, doctors are being advised to be aware of the possibility of heart issues in adolescents and young adults presenting with acute chest pain, shortness of breath, or palpitations after mRNA vaccination, according to ACIP Chair Grace Lee, MD, one of the presenters.

Meantime, the Food and Drug Administration plans to add a warning about these rare cases in young people to fact sheets for the Pfizer and Moderna COVID-19 vaccines, Reuters reported.

It's only natural to have questions and concerns about this. Here's what you need to know about the possible association between heart inflammation and the mRNA vaccines.

What is myocarditis?

Myocarditis is inflammation of the myocardium, the muscles in the heart, according to MedlinePlus, a service of the National Library of Medicine. When someone has myocarditis, the heart muscle becomes thick and swollen.

Myocarditis typically happens when an infection reaches the heart, usually a virus like the flu or adenovirus. But exposure to certain chemicals in the environment, radiation, autoimmune disorders, or reactions to medications like chemotherapy can also cause the condition. Bacterial infections like Lyme disease, streptococcus, and chlamydia can also lead to myocarditis, MedlinePlus says.

MedlinePlus lists the following as possible signs of heart inflammation:

  • Chest pain that can feel like a heart attack
  • Fatigue
  • Fever and other signs of infection including headache, muscle aches, sore throat, diarrhea, or rashes
  • Joint pain or swelling
  • Leg swelling
  • Pale, cool hands and feet
  • Rapid breathing
  • Rapid heart rate
  • Fainting
  • Not peeing as much as usual

What is pericarditis?

Similar to myocarditis, pericarditis is inflammation of the heart's pericardium, or the outer tissue that surrounds the heart, according to the American Heart Association (AHA). The pericardium's job is to hold the heart in place and help it work properly-it's actually made of two thin layers separated by a small amount of fluid to reduce friction as the heart beats.

Pericarditis can also be attributed to viral, bacterial, or fungal infections, but it's been linked to heart attack, heart surgery, or other medical conditions, injuries, or medications, too, the AHA says.

According to the National Heart, Lung, and Blood Institute (NHLBI), the following symptoms are associated with pericarditis:

  • Chest pain (this usually feels sharp, gets worse with breathing, and feels better when sitting up and leaning forward)
  • Fast heartbeat
  • Fever
  • Shortness of breath

Have myocarditis or pericarditis been linked with other vaccines?

Yes. "There have been rare reports of myocarditis after the flu vaccine," Richard Watkins, MD, an infectious disease physician and a professor of internal medicine at the Northeast Ohio Medical University, tells Health.

One 2018 case report published in the Journal of Cardiac Failure found that a heart transplant patient who had the flu vaccine developed myocarditis afterward. Another case report linked a 27-year-old woman's myocarditis to the flu vaccine she received three days before.

A short communication published in the International Journal of Cardiology in 2018 also found an association, although rare, between vaccinations and myocarditis or pericarditis. Researchers found that instances of both myocarditis and pericarditis-collected from the CDC's Vaccine Adverse Event Reporting System-were "extremely rare," and that "only in very few cases can a role of vaccine be actually identified." However, researchers did say that "vaccines against typhus, Japanese encephalitis, anthrax and meningococcus warrant monitoring."

How concerned should you be?

Doctors aren't overly worried, so you shouldn't be either. "We know that COVID-19 can cause myocarditis," John Sellick, DO, an infectious disease expert and professor of medicine at the University at Buffalo/SUNY, previously told Health. "But we've administered a huge number of the Pfizer vaccines in the US and we have not seen this."

Dr. Sellick points out that there's "always some background of this in the population" and that it's important to try to look at how often myocarditis happens among people under normal circumstances. About 3.1 million people in the world develop myocarditis each year, according to the Myocarditis Foundation.

Dr. Sellick also says he would be "very surprised" if there was a link between the vaccine and heart inflammation. "If this was a vaccine with a live virus, you might say that, in a certain group of people, perhaps their hearts go haywire," he says. "But with this vaccine, it seems biologically implausible."

Martin J. Blaser, MD, professor of medicine and pathology and laboratory medicine at the Rutgers Robert Wood Johnson Medical School in New Jersey, previously Health that it's important to remember that this is a "rare, rare event" and noted that people need to consider the risk versus the benefits of being vaccinated. "I want people to understand this."

Dr. Watkins agrees. "There is a far greater risk to the heart from COVID-19," he says.

Dr. Sellick urges people to stay calm. "Hopefully, this doesn't get blow out of proportion."

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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