Myocarditis, a rare complication of COVID-19 vaccination in teens and youth, is usually mild with fast clinical recovery

Myocarditis, or inflammation of the heart muscle, has been noted as a side effect of COVID-19 vaccination in adolescents and young adults, particularly in males. A national study co-led by Jane Newburger, MD, MPH, at Boston Children’s Hospital, and first author Dongngan Truong, MD, at the University of Utah and Primary Children’s Hospital (Salt Lake City), finds that symptoms are usually mild and usually subside quickly. However, because some young people had laboratory and cardiac MRI evidence of myocardial injury, the researchers urge continued monitoring for long-term heart effects in people who develop myocarditis after COVID-19 vaccination.

The study was published today in the journal Circulation.

“We found that teens and young adults who develop myocarditis following COVID-19 vaccination generally have mild symptoms that improve quickly,” says Jane Newburger, MD, MPH, associate cardiologist-in-chief at Boston Children's and the study’s senior investigator. “This rare complication of vaccination should be balanced against the greater risks of myocarditis, hospitalization, and other complications that occur with COVID-19 infection.”

The retrospective study, involving 26 pediatric centers across the U.S. and Canada, reviewed the cases of 139 patients, age 12 to 20 years, who had suspected myocarditis within 30 days of COVID-19 vaccination.

Ninety-one percent of cases occurred in males, and 98 percent were associated with mRNA vaccines. These were almost all with the Pfizer/BioNTech vaccine, as the FDA has not yet authorized the Moderna vaccine for children under 18. Ninety-one percent of cases occurred after the second vaccine dose. One patient had a very mild episode after his first vaccination and a more severe episode after his second vaccination.

Virtually all patients reported chest pain, 32 percent had fever, and 27 percent had shortness of breath. Symptoms began an average of two days after vaccination (the range was 0 to 22 days, but most developed symptoms between one and three days). Patients stayed in the hospital for an average of two days (range, 0 to 10 days), and 19 percent were admitted to an intensive care unit.

Of the 97 patients who had MRI imaging of their hearts, 75 (77 percent) had evidence of injury or inflammation of their heart muscle. Nineteen percent had weakened left-ventricular pumping function, but function normalized in all 25 patients who had follow-up assessments. No patient needed mechanical support, only seven had serious heart arrhythmias, and only two received drugs to boost their heart function.

The authors note that study was limited by its retrospective nature. No patients had heart biopsies to definitively diagnose myocarditis, and medical decisions on treatment and what kinds of testing to pursue were at the discretion of local clinicians. Also, because patients were seen at academic medical centers, their symptoms might have been worse than average.

“Findings of this study provide reassurance that youth who develop myocarditis after COVID-19 vaccination generally do well clinically, although long-term follow-up will be important to chart the course of recovery,” says Newburger. “Future research is needed to understand what factors makes some youth susceptible to this rare reaction to vaccination and how heart muscle injury occurs.”

The study was funded in part by the McCance Foundation and the Kostin Family Innovation Fund. See the paper for a complete list of authors.

About Boston Children’s Hospital

Boston Children’s Hospital is ranked the #1 children’s hospital in the nation by U.S. News & World Report and is the primary pediatric teaching affiliate of Harvard Medical School. Home to the world’s largest research enterprise based at a pediatric medical center, its discoveries have benefited both children and adults since 1869. Today, 3,000 researchers and scientific staff, including 10 members of the National Academy of Sciences, 25 members of the National Academy of Medicine and 10 Howard Hughes Medical Investigators comprise Boston Children’s research community. Founded as a 20-bed hospital for children, Boston Children’s is now a 415-bed comprehensive center for pediatric and adolescent health care. For more, visit our Answers blog and follow us on social media @BostonChildrens, @BCH_Innovation, Facebook and YouTube.

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