COVID-19 vaccine-related myocarditis in young people is mild and resolves quickly, research says

Adapted with permission from the American Heart Association.

Most young people under the age of 21 who developed suspected COVID-19 vaccine-related heart muscle inflammation known as myocarditis had mild symptoms that improved quickly, according to new research published today in the American Heart Association’s flagship journal Circulation.

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.

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 CDC definitions.

Of the 139 teens and young adults, ranging from 12 to 20 years of age, researchers identified and evaluated:

• Most patients were white (66.2%), nine out of 10 (90.6%) were male and median age was 15.8 years.
• Nearly every case (97.8%) followed an mRNA vaccine, and 91.4% 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 (99,3%); fever and shortness of breath each occurred in 30.9% and 27.3% of patients, respectively.
• About one in five patients (18.7%) was admitted to intensive care, but there were no deaths. Most patients were hospitalized for two or three days.
• More than three-fourths (77.3%) of patients who received a cardiac MRI showed evidence of inflammation of or injury to the heart muscle.
• Nearly 18.7% 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.

These data suggest that most cases of suspected COVID-19 vaccine-related myocarditis in people younger than 21 are mild and resolve quickly. 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.”

Dongngan T. Truong, M.D., study’s first author, associate professor of pediatrics, division of cardiology, University of Utah Health and pediatric cardiologist, Intermountain Primary Children’s Hospital in Salt Lake City

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. 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.

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