How worried should you be? We asked doctors.

By Korin Miller
April 26, 2021

Just days after the Centers for Disease Control and Prevention announced that it was lifting a pause on the Johnson & Johnson vaccine in the US over blood clot concerns, there's another report of a rare, potential side effect linked to a COVID-19 vaccine. This time, it's heart inflammation, aka myocarditis, associated with the Pfizer vaccine.

Israel's Health Ministry said on Sunday that it is looking into a small number of reported cases of heart inflammation in people who received the Pfizer COVID-19 vaccine. Israel's pandemic response coordinator, Nachman Ash, told Reuters on April 25 that a preliminary study found "tens of incidents" of myocarditis, a type of inflammation of the heart. Myocarditis was identified in 62 of the more than 5 million people in Israel who had received the Pfizer vaccine, usually after their second dose. The majority of patients are mostly men.

Credit: Getty Images / Design by Jo Imperio

According to a leaked report from the Israeli Health Ministry obtained by The Times of Israel, there have been 62 reported cases of myocarditis in patients who had the Pfizer vaccine. That puts the possible risk of getting myocarditis from the Pfizer vaccine, if there is indeed a link, at 0.001%.

Most cases happened in men under the age of 30, and two people have died, including a 22-year-old woman and 35-year-old man. Both reportedly were in good health before getting vaccinated.

Health reached out to Pfizer and received this response: "Pfizer is aware of the Israeli observations of myocarditis that occurred predominantly in a population of young men who received the Pfizer-BioNTech COVID-19 vaccine. We regularly meet with the Vaccine Safety Department of the Israeli Ministry of Health to review data. Adverse events are regularly and thoroughly reviewed and we have not observed a higher rate of myocarditis than what would be expected in the general population. A causal link to the vaccine has not been established. There is no evidence at this time to conclude that myocarditis is a risk associated with the use of Pfizer/BNT COVID-19 vaccine."

"More than 260 million doses of the Pfizer-BioNTech COVID-19 vaccine have been administered globally," states Pfizer's response. "Serious adverse events unrelated to, but close in timing to vaccination, are expected to occur at a similar rate in vaccinated individuals as they would in the overall population. With a vast number of people vaccinated to date, the benefit risk profile of our vaccine remains positive." 

Still, 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 Pfizer vaccine.

What is myocarditis, exactly?

Myocarditis is inflammation of the myocardium, the muscles in the heart, according to Medline Plus. 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, Medline Plus says.

What are the symptoms of myocarditis?

Medline Plus 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

Has myocarditis 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.

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, tells 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 Pfizer 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, tells Health that it's important to remember that this is a "rare, rare event" and that the link has not been proven. "There's no comparison between the risk and benefit of being vaccinated here," he says. "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. "This is an incredibly low risk, if the link is even proven," he says. "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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