Article Highlights

  • Heart inflammation, or myocarditis, has been reported as a very rare side effect of COVID-19 vaccines.


  • COVID-19 is more likely than vaccines to cause myocarditis, and symptoms and outcomes are often worse.

  • COVID-19 vaccines lower the risk of life-threatening heart problems and other serious health issues.

Americans received more than 590 million doses of COVID-19 vaccines between December 2020 and June 2022.1 The most intensive safety monitoring system in U.S. history has made it possible to detect even very rare COVID-19 vaccine side effects, including myocarditis, which is inflammation of the heart muscle. However, COVID-19 illness is far more likely to cause myocarditis than are the vaccines. That means the vaccines protect heart health.

Jerome Fleg, M.D., a program officer with the National Heart, Lung, and Blood Institute (NHLBI) Division of Cardiovascular Sciences, oversees and conducts research on heart disease. During the COVID-19 pandemic, Fleg turned his attention to the effects of SARS-CoV-2 infection on the heart, including myocarditis. We spoke with Fleg about the risk of myocarditis linked with COVID-19 illness and with vaccines.

What is myocarditis?

JEROME FLEG, M.D.: Myocarditis is an inflammation of the heart muscle. The walls of the heart become inflamed, which weakens the heart’s pumping action and can cause irregular heart rhythms, heart failure, and other complications. Viral infections, including COVID-19, are most often the cause,2 but other diseases, as well as some drugs and toxins, can also cause myocarditis.

The most common symptoms are chest pain, fever, fatigue, shortness of breath, and a rapid or irregular pulse. Some people may have minimal or no symptoms. Severe problems linked with myocarditis include chest pain, arrhythmias, trouble breathing, ankle or leg swelling, and fainting. Unfortunately, inflammation in the heart muscle can lead to serious complications, including heart failure, shock, or death.

Myocarditis usually goes away on its own with supportive care, including IV fluids, steroid therapy, and medicines to treat disorders of heart rhythm or pumping function. Treatment is often given in a hospital. For more severe cases of myocarditis caused by a virus, such as SARS-CoV-2, people may need to stay in the hospital for a week or two — often in the ICU. You can learn more about myocarditis symptoms, diagnosis, and treatment from the NHLBI.

“It’s clear that vaccination can protect you from myocarditis by protecting you from COVID-19 infection.” —Jerome Fleg, M.D.

Can COVID-19 cause myocarditis?

FLEG: Myocarditis is an uncommon complication of SARS-CoV-2 infection. We don’t know exactly how often this happens, but one study estimated that myocarditis affects about 40 people out of every 1,000,000 people who test positive for COVID-19.3 However, myocarditis is much more common in patients hospitalized for COVID-19 (226 per 100,000).

Some groups have a higher risk of developing myocarditis from COVID-19. An analysis of 51 patients with possible or confirmed myocarditis showed that 70% were male, and the average age was 56. Most had other health conditions, such as high blood pressure, diabetes, or obesity, that raised their risk for serious COVID-19 illness.4

Can COVID-19 vaccines cause myocarditis?

FLEG: Yes, but this is rare, and the symptoms are usually mild. Most people recover fully with rest and a few days of supportive treatment while being monitored in a hospital.

Men and boys between the ages of 16 and 29 have been most often affected by COVID-19–vaccine-related myocarditis, usually a few days after their second dose.5 Myocarditis may be due to their strong immune response to the vaccine.

It’s important to remember that any vaccine can cause side effects. These are normal signs that your body is making protective antibodies. Side effects of COVID-19 vaccination are generally mild — discomfort at the injection site, fatigue, and muscle aches — and go away in a few days. Many people have no side effects at all. Serious side effects are very uncommon. Myocarditis has been linked with other vaccines, such as those that prevent influenza (flu), smallpox, and shingles.6

Getting vaccinated to prevent severe COVID-19 cuts your risk of myocarditis. Myocarditis is very uncommon, but it has been on the rise since the pandemic began. Your chance of getting myocarditis after getting a COVID-19 vaccine is less than the chance of being struck by lightning during your lifetime. Data sources: Klamer et al., 2022; Cordero et al., 2022; National Weather Service.

Getting vaccinated to prevent severe COVID-19 cuts your risk of myocarditis. Myocarditis is very uncommon, but it has been on the rise since the pandemic began. Your chance of getting myocarditis after getting a COVID-19 vaccine is less than the chance of being struck by lightning during your lifetime. Data sources: Klamer et al., 2022; Cordero et al., 2022; National Weather Service.

Some people are unsure about getting a COVID-19 vaccine because of the risk of side effects, including myocarditis. Can you put these risks in perspective?

FLEG: The bottom line is this: The benefits of getting vaccinated markedly outweigh the very small risk of vaccine-related myocarditis. Vaccination prevents most hospitalizations and deaths due to COVID-19. It’s clear that vaccination can protect you from myocarditis by protecting you from COVID-19 infection.

Myocarditis is a rare complication of COVID-19 vaccination. It affects fewer than 20 people per 1,000,000 COVID-19 vaccinations.3,5,7 Only the mRNA vaccines (Pfizer-BioNTech and Moderna) have been linked with myocarditis. Myocarditis related to COVID-19 vaccines seems to be caused by the body’s immune response to vaccination.

Most people (95%) who develop myocarditis after receiving a COVID-19 mRNA vaccine have only mild symptoms that go away within a few days.5 Vaccine-linked myocarditis is less likely to cause lingering heart problems than myocarditis due to COVID-19 illness.

Only about 1 out of 100 cases of heart inflammation linked with COVID-19 vaccines is life-threatening.5 An analysis of 627 cases of vaccine-linked myocarditis worldwide showed that 626 fully recovered — and one fatality.7

The risk of myocarditis linked with COVID-19 illness is several times greater than the risk from vaccination, and it is often more serious.3,5,8 This is because the SARS-CoV-2 virus invades cells of the heart, plus the body generates an overactive immune response to the infection.

Severe myocarditis can cause long-lasting heart damage or even death. An analysis of almost 400 patients with myocarditis linked with COVID-19 illness found that about 15% died within 6 months.9

Myocarditis linked with COVID-19 illness may also be more severe because these patients are usually older and have other health conditions that increase their risk of complications. It’s also possible that myocarditis linked with vaccination is less serious because of the younger average age and healthier status of people getting vaccinated.

Why didn’t the testing of the COVID-19 vaccines show a risk of myocarditis?

FLEG: Tens of thousands of people participated in the clinical trials for the COVID-19 vaccines. Even though the studies were among the largest vaccine trials in history, they were not large enough to detect very rare complications like myocarditis that occur only a few times per million vaccinations.

If you have any health problems after vaccination, report them to the Vaccine Adverse Event Reporting System. People who experience a serious side effect of a vaccine or other medical products for COVID-19 may be eligible for compensation under the federal Countermeasures Injury Compensation Program.

If you have any health problems after vaccination, report them to the Vaccine Adverse Event Reporting System. People who experience a serious side effect of a vaccine or other medical products for COVID-19 may be eligible for compensation under the federal Countermeasures Injury Compensation Program.

What should adults and young adults think about when they are deciding whether to get vaccinated?

FLEG: Vaccination helps protect people from getting sick or severely ill with COVID-19 and helps protect those around them.

Myocarditis is rare, but it occurs more often following SARS-CoV-2 infection than after receiving an mRNA COVID-19 vaccine for people of all ages.10

We know that boys and men between the ages of 16 and 29 have a higher risk of COVID-19–vaccine-related myocarditis. Even in this group, though, heart inflammation is seven or eight times more common after SARS-CoV-2 infection.10 And the data suggest that young adults with myocarditis possibly linked with COVID-19 vaccines recover quickly with supportive care.11

I’d really like everyone to understand that the benefits of the COVID-19 vaccines strongly outweigh the very small risk of serious side effects. The vaccines are very effective against severe COVID-19 and protect your heart from the serious health consequences of the disease. Your health care provider can provide more information that’s specific to your situation.

What factors should parents think about when deciding whether to vaccinate their children?

FLEG: The CDC (Centers for Disease Control and Prevention) recommends COVID-19 vaccination for children as young as 6 months. Parents should speak with their children’s health care providers regarding the benefits and risks of vaccination against COVID-19. Key factors to consider are the current rates of COVID-19 infection, the child’s overall health, and the parents’ assessment of risks.

Among teenaged boys — the group with the highest risk of myocarditis after COVID-19 vaccination — the risk is between 2 and 5 times higher after SARS-CoV-2 infection than after vaccination.10

A study of children ages 12 to 17 in England estimated that COVID-19 vaccination prevented 4,500 hospitalizations, 300 ICU hospital stays, and 36 deaths during the summer of 2021 when infection rates were high.11

Children with myocarditis linked with vaccination are less likely to be hospitalized, admitted to the ICU, or need ventilator support, compared with children who had myocarditis after a COVID-19 diagnosis. They also recover normal heart function sooner.12

The Journey of a Vaccine

Learn about the four phases of clinical research, what questions researchers try to answer in each, and how a vaccine is developed, approved, and manufactured.

What research is the NHLBI supporting on COVID-19 and myocarditis?

FLEG: The NHLBI has a strong history of conducting and funding research on myocarditis. Between 2001 and 2020, the Institute has funded 139 myocarditis studies at a cost of $43.6 million. Six awards are related to COVID-19–related myocarditis.

We’re currently supporting two large studies looking at long-term effects of COVID-19, including myocarditis and other heart conditions. The Researching COVID to Enhance Recovery (RECOVER) Initiative is taking place at 80 centers across the country. The scientists are monitoring the health of a diverse group of people to learn about the long-term effects of COVID, including heart problems. The CONNECTS-Collaborative Cohort of Cohorts for COVID-19 Research (CONNECTS-C4R) trial is enrolling 50,000 people to determine factors that may predict disease severity and long-term side effects of COVID-19. Because these studies are in their early phases, the results are not ready yet.

Another study is enrolling 500 survivors of COVID-19 to monitor their hearts for long-term effects of COVID-19, using cardiac MRI and echocardiography scans.

NHLBI-supported research aims to identify the causes of lasting heart and lung symptoms of COVID-19, find ways to prevent these problems, and improve treatment to promote rapid healing.

Sources

  1. Centers for Disease Control and Prevention. (2022). COVID-19 Vaccinations in the United States. Accessed June 29, 2022, from https://covid.cdc.gov/covid-data-tracker/#vaccinations_vacc-total-admin-rate-total.
  2. Law, Y. M., Lal, A. K., Chen, S., Čiháková, D., Cooper, L. T., Jr, Deshpande, S., Godown, J., Grosse-Wortmann, L., Robinson, J. D., Towbin, J. A., & American Heart Association Pediatric Heart Failure and Transplantation Committee of the Council on Lifelong Congenital Heart Disease and Heart Health in the Young and Stroke Council (2021). Diagnosis and Management of Myocarditis in Children: A Scientific Statement from the American Heart Association. Circulation, 144(6), e123–e135. https://doi.org/10.1161/CIR.0000000000001001
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  4. Ho, J. S., Sia, C.-H., Chan, M. Y., Lin, W., & Wong, R. C. (2020). Coronavirus-induced myocarditis: A meta-summary of cases. Heart & Lung: The Journal of Critical Care, 49(6), 681–685. https://doi.org/10.1016/j.hrtlng.2020.08.013
  5. Klamer, T. A., Linschoten, M., & Asselbergs, F. W. (2022). The benefit of vaccination against COVID-19 outweighs the potential risk of myocarditis and pericarditis. Netherlands Heart Journal: Monthly Journal of the Netherlands Society of Cardiology and the Netherlands Heart Foundation, 30(4), 190–197. https://doi.org/10.1007/s12471-022-01677-9
  6. Su, J. R., McNeil, M. M., Welsh, K. J., Marquez, P. L., Ng, C., Yan, M., & Cano, M. V. (2021). Myopericarditis after vaccination, Vaccine Adverse Event Reporting System (VAERS), 1990-2018. Vaccine, 39(5), 839–845. https://doi.org/10.1016/j.vaccine.2020.12.046
  7. Cordero, A., Cazorla, D., Escribano, D., Quintanilla, M. A., López-Ayala, J. M., Berbel, P. P., & Bertomeu-González, V. (2022). Myocarditis after RNA-based vaccines for coronavirus. International Journal of Cardiology, 353, 131–134. https://doi.org/10.1016/j.ijcard.2022.01.037
  8. Chou, O., Zhou, J., Lee, T., Kot, T., Lee, S., Wai, A., Wong, W. T., Zhang, Q., Cheng, S. H., Liu, T., Vassiliou, V. S., Cheung, B., & Tse, G. (2022). Comparisons of the risk of myopericarditis between COVID-19 patients and individuals receiving COVID-19 vaccines: a population-based study. Clinical Research in Cardiology: Official Journal of the German Cardiac Society, 1–6. https://doi.org/10.1007/s00392-022-02007-0
  9. Annie, F. H., Alkhaimy, H., Nanjundappa, A., & Elashery, A. (2022). Association Between Myocarditis and Mortality in COVID-19 Patients in a Large Registry. Mayo Clinic Proceedings. Innovations, Quality & Outcomes, 6(2), 114–119. https://doi.org/10.1016/j.mayocpiqo.2021.12.006
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Page last updated: July 5, 2022