Heart Inflammation a 'Rare' Side Effect of mRNA COVID-19 Vaccines in Young People, Says the CDC

Vaccination is still recommended for everyone 6 months and older.

Beginning in April 2021, there was an increase in the number of cases of myocarditis and pericarditis reported in the United States. These cases of myocarditis (or inflammation of the heart) and pericarditis (inflammation of the tissue surrounding the heart) occurred most often within a week after the second dose of the Pfizer and Moderna vaccines, and in young adult males ages 16 years and older, according to the Centers for Disease Control and Prevention (CDC).

The CDC reported a rate of 12.6 cases per million second doses of Pfizer's or Moderna's vaccine within three weeks following vaccination among 12- to 39-year-olds. This link was identified based on data reported to the Vaccine Adverse Event Reporting System (VAERS), the nation's early warning system for vaccine safety, and other surveillance activities.

As of August 2022, VAERS received 1,022 preliminary reports of myocarditis or pericarditis in people 18 and younger who received a COVID vaccine, mostly the mRNA vaccines, according to the CDC. Of those, the agency has confirmed 672 cases of myocarditis.

Scientists noted that these problems appear to be rare and mostly not serious. The CDC and Advisory Committee on Immunization Practices (ACIP) have determined that the benefits of receiving the mRNA COVID-19 vaccines outweigh the slightly increased risk of myocarditis and pericarditis.

The CDC continues to recommend vaccination for everyone 6 months and older, along with boosters for all eligible individuals 5 years and older.

To reduce the risk of myocarditis associated with the mRNA COVID-19 vaccines, the CDC says waiting eight weeks between the first two doses may be optimal for some people ages 6 months to 64 years—particularly for males ages 12 to 39 years.

Healthcare providers 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. In June 2021, the Food and Drug Administration (FDA) announced an update to the Moderna and Pfizer COVID-19 vaccine fact sheets for healthcare providers and vaccine recipients and caregivers about the rare risk of developing myocarditis and pericarditis.

It's only natural to have questions and concerns about this. Here's what you need to know about the 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 such as headache, sore throat, muscle aches, diarrhea, or rashes
  • Joint pain or swelling
  • Swelling in the legs
  • 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, worsens with breathing, and feels better when sitting up and leaning forward)
  • Fast-beating heart
  • 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, told 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 published in Acute and Critical Care in 2019 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. According to the CDC, myocarditis and pericarditis after COVID-19 vaccination are rare, and most people who developed these conditions have responded well to medication and rest.

Dr. Sellick also pointed 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. According to the Myocarditis Foundation, about 3.1 million people in the world were diagnosed with myocarditis in 2017 alone.

Martin J. Blaser, MD, professor of medicine and pathology and laboratory medicine at the Rutgers Robert Wood Johnson Medical School in New Jersey, previously told 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 agreed. "There is a far greater risk to the heart from COVID-19," he said.

That said, if you have concerns about COVID-19 vaccination, be sure to talk with a healthcare provider about it. If you suspect that you or your child are experiencing symptoms of myocarditis or pericarditis—especially if it's within a week after receiving a COVID-19 vaccine—seek medical attention right away.

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 CDC, WHO, and their local public health department as resources.

Updated by
Karen Pallarito
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Karen is a senior editor at Health, where she produces health condition “explainers” backed by current science. 
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