Myocarditis after weak Covid vaccine in adolescents and young adults, large study finds

The incidence of myocarditis and pericarditis after Covid vaccination is low and most patients recover fully, according to a large international study from Nationwide Children’s Hospital.

Most cases have occurred in adolescent and young adult males and typically after the second dose of a primary series of the Pfizer-BioNTech or Moderna vaccine, according to the study published Monday in JAMA Pediatrics.

Although the majority of people recovered quickly, 93% of cases required hospitalization and 23% of cases were severe enough to require admission to an intensive care unit. No deaths were observed.

While the study results are “reassuring,” vaccine-associated heart problems “should not be considered always mild,” said Dr. Dan Barouch, director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical. Center in Boston. He did not participate in the research.

The results confirm previous studies which found that myocarditis, an inflammation of the heart muscle, and pericarditis, an inflammation of the outer lining of the heart, after vaccination against Covid are rare.

But many of these studies, the authors wrote, relied on self-reporting to safety monitoring systems and contained populations from certain countries, where people may have similar risk factors.

Researchers from Nationwide Children’s Hospital reviewed 23 peer-reviewed studies through August across multiple locations, including the United States, Hong Kong, South Korea and countries in Europe.

The review included more than 800 adolescents and young adults who developed myocarditis and pericarditis after vaccination against Covid.

Heart-related conditions generally occurred within four days of the second dose of a Covid vaccine, the study found.

What are the symptoms of myocarditis?

The most common symptoms were:

  • Chest pain

  • Fever

  • Headache

  • Shortness of breath

According to the study, levels of troponin, specific proteins that can indicate heart problems, including heart damage, were elevated in about 84% of patients.

Most patients recovered with rest and medication. However, 87% had abnormalities on their cardiac MRIs, raising the question of whether there could be any long-term consequences for the disease, Barouch said.

Pfizer and Moderna are both running long-term clinical trials to track health issues — if any — in the years following a diagnosis of vaccine-associated heart problems in adolescents and young adults.

The research has limitations, including that some of the studies reviewed were observational, meaning they cannot prove cause and effect. The researchers were also unable to determine whether the timing between doses influenced disease incidence. (Studies have shown that a wider gap between doses may reduce the risk of inflammation.)

It also doesn’t address what makes young men more susceptible to heart-related health problems, although some experts expect the virus’ spike protein, once produced in the cell after vaccination, can 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 risk estimates for myocarditis by age, sex, type of vaccine and spacing 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 disease occurrence to be low at 0, 3 to 5 cases per 100,000 people vaccinated.

It’s important to note that Covid vaccines aren’t the only vaccines that have been linked to myocarditis, said Dr. Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia.

This has also been seen after the smallpox vaccination, he said, although the number of cases may seem higher after the Covid vaccines because “we are paying a lot 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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