Post-Vaccine Myocarditis in Young People is Rare and Usually Mild, New Study from Researchers in Utah and Boston Finds

Most young people under the age of 21 who developed suspected COVID-19 vaccine-related heart muscle inflammation known as myocarditis had mild symptoms and findings that improved quickly, according to new study by researchers in Utah and Boston recently published in Circulation, the journal of the American Heart. 

Myocarditis is a rare but serious condition that causes inflammation of the heart muscle. It can weaken the heart and affect the heart’s electrical system, which keeps the heart pumping regularly. It is most often the result of an infection and/or inflammation caused by a virus.

Research Finding Highlights:

  • Most adolescents and young adults with suspected myocarditis following COVID-19 vaccination experience mild symptoms and rapid clinical recovery, though many had evidence of heart inflammation on testing, according to a new study published today.
  • Study authors said fast ventricular rhythms were uncommon, and no patients died or needed mechanical support for circulation as a result of the condition.
  • While cases of myocarditis following COVID-19 vaccinations continue to be rare, more research is needed to understand whether there are long-term cardiac effects of COVID-19-vaccine-associated myocarditis.

“These data suggest that most cases of suspected COVID-19 vaccine-related myocarditis in people younger than 21 are mild and resolve quickly,” said study author Dongngan T. Truong, MD, associate professor of pediatrics in the division of cardiology at University of Utah Health and a pediatric cardiologist at Intermountain Primary Children’s Hospital

“We were very happy to see that type of recovery;  however, we are awaiting further studies to better understand the long-term outcomes of patients who have had COVID-19 vaccination-related myocarditis. We also need to study the risk factors and mechanisms for this rare complication,” she added.

“The highest rates of myocarditis following COVID-19 vaccination have been reported among adolescent and young adult males. Past research shows this rare side effect to be associated with some other vaccines, most notably the smallpox vaccine,” said the study’s senior author, Jane W. Newburger, MD, MPGH, FAHA, associate chair of academic affairs in the Department of Cardiology at Boston Children’s Hospital, the commonwealth professor of pediatrics at Harvard Medical School, and member of the American Heart Association Young Hearts Council. 

“While current data on symptoms, case severity and short-term outcomes is limited, we set out to examine a large group of suspected cases of this heart condition as it relates to the COVID-19 vaccine in teens and adults younger than 21 in North America,” Dr. Newburger added. 

Using data from 26 pediatric medical centers across the United States and Canada, researchers reviewed the medical records of patients younger than 21 who showed symptoms, lab results or imaging findings indicating myocarditis within one month of receiving a COVID-19 vaccination, prior to July 4, 2021. 

Cases of suspected vaccine-associated myocarditis were categorized as “probable” or “confirmed” using known CDC definitions. Of the 139 teens and young adults, ranging from 12 to 20 years of age, researchers identified and discovered the following:

  • Most patients were white (66.2%); nine out of 10 (91%) were male.
  • Nearly every case (98%) followed an mRNA vaccine, and 91% occurred after the second vaccine dose.
  • Onset of symptoms occurred at a median of 2 days following vaccine administration.
  • Chest pain was the most common symptom (99%); fever and shortness of breath each occurred in 30.9% and 27.3% of patients, respectively.
  • About one in five patients (19%) was admitted to intensive care, but there were no deaths. Most patients were hospitalized for two or three days.
  • More than three-fourths (77%) of patients who received a cardiac MRI showed evidence of inflammation of or injury to the heart muscle.
  • Nearly 19% had at least mildly decreased left ventricular function (squeeze of the heart) at presentation, but heart function had returned to normal in all who returned for follow-up.

Researchers say future studies should follow patients who have suffered vaccine-associated myocarditis over a longer term, since this study examined only the immediate course of patients and lacks follow-up data. 

Additionally, there are several important limitations to consider. The study design did not allow scientists to estimate the percentage of those who received the vaccine and who developed this rare complication, nor did it allow for a risk/benefit ratio examination. 

Because the patients included in this study were also evaluated at academic medical centers and may have been more seriously ill than other cases found in a community, researchers note.

“It is important for health care providers and the public to have information about early signs, symptoms, and time course of recovery, particularly as these vaccines become more widely available to children,”  Dr. Truong said.  “Studies to determine long-term outcomes in those who have had myocarditis after COVID-19 vaccination are also planned.”

Researchers recommend that caregivers consider myocarditis in individuals presenting with chest pain after receiving a COVID-19 vaccine, especially in boys and young men in the first week after the second vaccination.

“These findings also support the American Heart Association’s position that COVID-19 vaccines are safe, highly effective and fundamental to saving lives, protecting our families and communities against COVID-19, and ending the pandemic. Please get your child vaccinated as soon as possible,” said Donald. M. Lloyd-Jones, MD, president of the American Heart Association, who was not involved in the study. 



New study published in Circulation, the journal of the American Heart.