Most Cases of Vaccine-Associated Myocarditis Have Mild Course, Resolve Quickly

Dongngan Truong, MD

New research suggests most cases of suspected COVID-19 vaccine myocarditis in younger patients had a mild clinical course with symptoms that resolved quickly.

An analysis leveraging data from 26 pediatric medical centers in the US and Canada, results of the study suggest fewer than 1-in-5 patients were admitted to intensive care, 0 deaths occurred, and most patients were hospitalized for 2-3 days. Results of the analysis also provide insight into the treatment course as well as abnormal laboratory and imaging findings among these patients.

“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 investigator Dongngan Truong, MD, an associate professor of pediatrics in the division of cardiology at the University of Utah and a pediatric cardiologist at Intermountain Primary Children’s Hospital, in a statement from the American Heart Association (AHA). “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.”

As the pandemic has moved forward, a byproduct of it has been the ever-changing spotlight focused on specific topics related to COVID-19. For example, in Spring 2020, focus was on the potential for blood clots. Fast-forward to now and one of the main topics of discussion related to vaccine safety is now focused on the potential risk of myocarditis and pericarditis associated with mRNA vaccines.

To develop a better understanding of the clinical course and short-term outcomes of vaccine-related myocarditis, Truong and a team of colleagues from multiple institutions designed the current study as a retrospective analysis of data from patients younger than 21 years of age with suspected myocarditis within 30 days of COVID-19 vaccination from 26 centers in the US and Canada. As of July 4, 2021, investigators identified 146 episodes of clinically suspected vaccine-associated myocarditis among 145 adolescents. From this, 6 patients were excluded due to lack of abnormal troponin and 140 episodes in 139 patients were included in final analyses.

This cohort was 66.2% White, 69.1% non-Hispanic, and 90.6% male. The median age of patients in the cohort was 15.8 (IQR, 14.5-17.0) years and age of patients ranged from 12.1-20.3 years. Investigators determined 35% of episodes met criteria for confirmed myocarditis and the remaining would be classified as probable. For the purpose of analysis, Lake Louise criteria were used for cMRI findings and myocarditis cases were classified as confirmed or probable according to CDC definitions.

Of the 139 patients included in final analyses, 131 (94.2%) received the Pfizer-BioNTech vaccine, 5 (3.6%) received the Moderna vaccine, 1 (0.7%) received the Johnson and Johnson vaccine, and the brand of vaccine was unknown for 2 patients. Most patients (91.4%) developed suspected myocarditis following the second dose. The median onset of symptoms occurred 2 days after vaccination and the most common symptom was chest pain, which occurred in all but 1 of the 139 patients.

Of the 139 patients, 81.3% received treatment with non-steroidal anti-inflammatory drugs, 21.6% received IV immunoglobulin, 21.6% received glucocorticoids, 7.9% received coaching, and 8.6% received no anti-inflammatory therapies. Overall, 26 (18.7%) of patients required intensive care and 2 were treated with inotropic/vasoactive support, but none required ECMO or died. The median hospital stay was 2 (IQR, 2-3) days and the range was 0-10 days.

Further analysis suggested all patients had elevated troponin I (median: 8.12 ng/mL, IQR 3.50-15.90 ng/mL; n=111) or T (median: 0.61 ng/mL, IQR 0.25-1.3 ng/mL; n=28). Additionally, 97 (69.8%) of patients had abnormal ECGs, with 7 experiencing nonsustained ventricular tachycardia, and 18.7% had LVEF below 55%. Among a cohort of 97 patients who underwent cMRI at a median of 5 days from symptom onset, 75 (77.3%) had abnormal findings, including 74 (76.3%) with late gadolinium enhancement, 54 (55.7%) with myocardial edema, and 49 (50.5%) meeting Lake Louise criteria. Investigators also noted a cohort of 26 patients with LVEF below 55% on echocardiogram all had normalized function at follow-up.

“In June of this year, the U.S. Centers for Disease Control and Prevention (CDC) Advisory Committee on Immunization Practices reported a likely link between mRNA COVID-19 vaccination and myocarditis, particularly in people younger than 39. However, research continues to find COVID-19 vaccine-related cases of myocarditis uncommon and mostly mild,” said Donald M. Lloyd-Jones, MD, ScM, president of the AHA, who was not involved in the study. “Overwhelmingly, data continue to indicate that the benefits of COVID-19 vaccination – 91% effective at preventing complications of severe COVID-19 infection including hospitalization and death – far exceed the very rare risks of adverse events, including myocarditis.”

This study, “Clinically Suspected Myocarditis Temporally Related to COVID-19 Vaccination in Adolescents and Young Adults,” was published in Circulation.