The incidence of myocarditis and pericarditis after Covid vaccination is low and most patients recover completely, a large international study from Nationwide Children’s Hospital has found.
Most cases occurred in adolescent and young adult males and usually after the second dose of a primary series of Pfizer-BioNTech or Moderna vaccines, according to the study published Monday in JAMA Pediatrics.
Although most people recovered quickly, 93% of cases required hospitalization and 23% of cases were severe enough to require ICU admission. No deaths were observed.
While the study results are “reassuring,” heart problems associated with the vaccine “shouldn’t always be considered mild,” said Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston. He was not involved in the research.
The findings confirm previous studies that found myocarditis, an inflammation of the heart muscle, and pericarditis, an inflammation of the outer lining of the heart, following the Covid vaccination are rare.
But many of these studies, the authors wrote, relied on self-report to safety surveillance systems and contained populations from certain countries, where people may have similar risk factors.
Researchers at Nationwide Children’s Hospital looked at 23 peer-reviewed studies through August in multiple locations, including the United States, Hong Kong, South Korea and European countries.
The review included more than 800 adolescents and young adults who developed myocarditis and pericarditis following the Covid vaccination.
Heart conditions usually occurred within four days of a second dose of a Covid vaccine, the study found.
What are the symptoms of myocarditis?
The most common symptoms were:
Shortness of breath
Levels of troponin, a specific protein that can indicate problems with the heart, including heart injury, were elevated in about 84 percent of patients, according to the study.
Most patients recovered with rest and medication. However, 87 percent had cardiac MRI abnormalities, raising the question of whether there could be long-term consequences for the condition, Barouch said.
Pfizer and Moderna are both conducting long-term clinical trials to monitor for health problems in the years following a diagnosis of vaccine-associated heart problems in adolescents and young adults.
The research has limitations, including the fact that some of the studies reviewed were observational, meaning they can’t prove cause and effect. The researchers also were unable to determine whether the timing between doses influenced the incidence of the condition. (Studies have found that a wider interval between doses can reduce the risk of the inflammatory condition.)
It also does not address what makes young men more susceptible to heart-related health conditions, although some experts expect that the spike protein of the virus, once made in the cell following vaccination, could generate a reaction in the body that can cause inflammation in the heart.
Daniel Salmon, director of the Institute for Vaccine Safety at Johns Hopkins University, said he would still like to see myocarditis risk estimates by age, gender, vaccine type and distance between doses.
The study authors said the overall incidence of myocarditis after COVID vaccination was consistent with estimates from the United States and Israel, which found the occurrence of the condition was low, ranging from 0.3 to 5 cases. per 100,000 people vaccinated.
It’s important to note that the Covid vaccines aren’t the only vaccinations that have been linked to myocarditis, said Dr. Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia.
It has also been seen after smallpox vaccination, he said, although the number of cases may appear higher after the Covid vaccines because “we’re paying much more attention.”
The authors also noted that the risk of developing myocarditis after Covid infection is significantly higher than after vaccination.
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This article was originally published on NBCNews.com