Cases of post-COVID-19 vaccine myocarditis, swelling of the heart muscle, in people under 21 are rare and usually mild, a study published Dec. 6 in Circulation confirmed.
The CDC's Advisory Committee on Immunization Practices held an emergency meeting in June after 475 cases of myocarditis following mRNA COVID-19 vaccination were reported to the agency, particularly in people under 39. Most fully recovered from their symptoms.
Researchers analyzed data from 26 pediatric medical centers in the United States and Canada to examine cases of suspected myocarditis in people under 21.
Suspected myocarditis occurred in 136 patients after mRNA vaccination, with 131 after the Pfizer-BioNTech vaccine; 91.4 percent of cases occurred after the second dose. Symptoms appeared a median two days after vaccination, with the most common being chest pain.
The median hospitalization time was two days, with 26 patients ending up in intensive care. No deaths were reported.
"These data suggest that most cases of suspected COVID-19 vaccine-related myocarditis in people younger than 21 are mild and resolve quickly," Dongngan T. Truong, MD, the study's principal author and associate professor of pediatrics in the division of cardiology at the University of Utah in Salt Lake City, said in a news release
The study's authors noted a limitation was that the study's design did not allow researchers to estimate the incidence or risk of myocarditis in adolescents and young adults after COVID-19 vaccination, or to compare these risks with those from severe cardiac effects in youth after acute COVID-19 or MIS-C.