In the two years since the COVID vaccines became available to the public, they have become a popular target for misinformation. Anti-vaccine activists have made some wild claims—the vaccines alter DNA, cause infertility, and implant magnetic devices for the government to track your every move—with no credible scientific evidence. But they have managed to accomplish one goal: More Americans than ever are hesitant about getting a vaccine.

So whenever a person has a rare side effect from the COVID vaccines, news spreads rapidly. For example, Florida’s surgeon general recommended boys between 18 to 39 should not get the mRNA shots, citing a questionable state analysis that claimed the risk of cardiac death jumped up by 84 percent after immunization. More recently, people were quick to blame Buffalo Bills player Damar Hamlin’s sudden cardiac arrest in early January on the NFL’s mandatory COVID vaccine requirement. Cardiologists, however, were just as quick to debunk the notion with more realistic medical explanations.

Infectious disease experts have been investigating the risk of myocarditis since the beginning of the pandemic. Thousands of studies have been published on COVID, and some have found a connection between myocarditis with both the virus and the vaccines. Here are the answers we have so far.

What is myocarditis?

Myocarditis is a disease that causes inflammation in a middle layer of the heart muscle called the myocardium. The inflammation affects muscle cell function and the heart’s electrical system, causing irregular heart beats and interfering with pumping blood to and from the body. The inflammation results from your body’s immune response overreacting to an infection it’s currently fighting. Viruses are the common cause of most myocarditis infections and are responsible for 1.5 million cases every year.

A majority of myocarditis cases are mild and self-resolving, says Keren Hasbani, a pediatric cardiologist at Pediatrix Pediatric and Congenital Cardiology Associates of Texas. Most go away in less than two weeks without complications or need to go to the hospital. 

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Myocarditis persisting for longer than two weeks is considered chronic and can create severe complications. The longer inflammation stays in the heart, the weaker the muscle becomes. Continued injuries to heart cells can lead to permanent scarring of cardiac tissue, which can cause the condition to come back and increase the risk of stroke, heart attack, heart failure, or death.

Myocarditis can strike anyone, at any age. However, the heart condition appears to occur at twice the rate in young men than women.

What does myocarditis feel like?

In some myocarditis cases, it is possible for a person to go about their day without knowing that their heart is inflamed. When there are symptoms, they could mimic those of a viral infection, including fever, vomiting, headaches, and a sore throat. 

The most common presenting sign of the condition is a discomfort or a feeling of tightening in the chest area. Hasbani says the pain can happen anywhere between your left side to the chest bone area. Rather than the soreness you feel when you pull a pectoral muscle, Hasbani says myocarditis chest pain is often described as aches originating from a place much deeper inside the body. “People usually say it’s different from any kind of chest pain they’ve felt before.”

Angioplasty heart exam seen in multiple small black and white images
Pain that results from myocarditis often feels distinct from other chest aches and pains. Deposit Photos

Individuals with myocarditis also tend to describe rapid or abnormal heart beats because the inflammation affects the heart’s electrical system. Since the organ is not functioning to its full potential, blood is not being properly distributed to other parts of the body. This can lead to symptoms such as shortness of breath, especially as the chest pain makes it difficult to take big deep breaths. The lack of oxygen can then spur on lightheadedness and fainting spells. Less common symptoms include swelling in the legs, ankles, and feet from the lack of blood distribution.

While Hasbani says it’s extremely rare, myocarditis can be life-threatening when the weakened heart cannot meet the demands of the body. In these scenarios, a person would need to be hospitalized and given medication such as adrenaline to keep the heart pumping. Doctors may also have to provide a life support machine to oxygenate and pump the blood. This allows the heart to rest and recover from the damage myocarditis inflicted. 

Is there a relationship between myocarditis and COVID?

COVID infections can cause severe and life-threatening cases of myocarditis, but the overlap is still slim. Forty out of every 1 million people are estimated to develop myocarditis 28 days after testing positive. The chances of inflammation increases among people with severe COVID illness that requires hospitalization and people with preexisting health conditions such as high blood pressure and obesity.

A 2021 study from the Centers for Disease Control and Prevention (CDC) found the risk of myocarditis is 16 times higher among unvaccinated people with COVID than unvaccinated people who have never had the disease. It also found that men and adults 50 years and older are more vulnerable to the condition. Among unvaccinated children under 16, myocarditis risk was 37 times higher in those with COVID infection than their healthy peers. 

[Related: What patients find at long COVID clinics: rejection, outdated therapies, and unanswered questions]

Hasbani says the reason why people with myocarditis from a COVID infection have more serious complications is because the body is already overworked from dealing with the extensive damage the virus is causing to other organs like the lungs, kidneys, and GI tract. Inflammation in the heart may take a backseat to all the other ongoing bodily issues and take longer to resolve. In children under 16, the CDC speculates that COVID-induced myocarditis might actually be a sign of multisystem inflammatory syndrome, which is a potentially deadly condition associated with the coronavirus. 

Can COVID vaccines cause myocarditis?

Yes, but the chances are extremely rare. One August 2022 study in England calculated the rate of hospitalizations and deaths related to myocarditis in more than 42 million people 13 and older. The subjects consisted of two different groups: individuals fully vaccinated with either the AstraZeneca, Moderna, or Pfizer-BioNTech vaccines, and unvaccinated individuals who tested positive for COVID. The researchers found a 0.007-percent chance—that’s 2,681 out of 43 million vaccinated adultsof being hospitalized or dying from vaccine-related myocarditis. Only 0.001 percent occurred within 28 days of receiving a COVID vaccine or booster. A separate study from October 2022 estimated that the myocarditis risk is seven times greater in unvaccinated versus vaccinated individuals. 

So far only the mRNA vaccines have been associated with myocarditis. The risk appears to be higher in people with a second dose of the Moderna shot than the Pfizer-BioNTech one, says Jayne Morgan, a cardiologist and clinical director of the COVID task force at Piedmont Hospital in Atlanta. The large-scale study done in England last year showed more overlap of myocarditis cases with a second Moderna dose. Meanwhile, another 2022 study measured a two- to threefold higher chance of developing myocarditis after a second Moderna vaccine, with the association being the strongest among men and people between 18 to 39. Still, Morgan warns that the rate is small compared to that of unvaccinated populations with COVID.

[Related: The truth about COVID, vaccines, ED, and infertility]

Though incidence is low, research points to young men under 40 having the highest risk of developing myocarditis, says Morgan. A September 2022 study in Israel reported 28 mild cases of myocarditis after a the Pfizer-BioNTech booster shot—out of nearly four million adults. The results showed that men between the ages of 16 to 19 had the highest risk of myocarditis (a 1 in 15,000 chance), followed by men between the ages of 20 to 24. All individuals made a full recovery after spending an average of 3.5 days in the hospital.

There is no official explanation for why young men have a greater risk of myocarditis. Some COVID researchers have hypothesized that the SARS-CoV-2 spike protein that the mRNA vaccines were designed from might trigger an overly active immune response that causes inflammation in the heart. That doesn’t mean the vaccine causes the infection, warns Hasbani: Instead, the immune system is responding to the vaccine in a way that also happens to react with heart cells in the myocardium. The effect is nearly always temporary.

Myocarditis existed well before COVID vaccines

Hasbani says any medical treatment, including vaccines, has side effects, including ones that involve the heart. The smallpox vaccine, for example, helped eliminate smallpox worldwide in 1980, but was later found to have a 10-percent risk of mild myocarditis.

One likely reason we know more about the risks of myocarditis for the COVID vaccine is that “we haven’t vaccinated this amount of people this quickly for one specific illness, and followed a large population this closely,” Hasbani explains.

With all the facts, both experts stress that the small risk of myocarditis does not outweigh the severe complications you can get from a SARS-CoV-2 infection. For instance, long COVID remains an issue for millions of patients and has been associated with far more persisting heart problems. “Giving you and your family a vaccine is much safer than taking your chance on COVID,” Hasbani adds.

If the vaccine does cause cardiac inflammation in someone, there is little chance the condition would cause a heart failure. A January 2022 analysis of more than 17 million people found just 627 cases (or 0.0035 percent) of COVID vaccine-related myocarditis. Of those, 626 individuals fully recovered and one individual died. To put that into perspective, the National Institute of Health website states: “Your chance of getting myocarditis after getting a COVID vaccine is less than the chance of being struck by lightning during your lifetime.”