F.D.A. Is Reviewing If Moderna Vaccine Causes Heart Problems in Adolescents

Moderna said more than 1.5 million adolescents worldwide have received its coronavirus vaccine, and the data thus far do not suggest an increased risk of myocarditis. But studies from Israel and the United States have linked both the Pfizer-BioNTech and Moderna vaccines to rare and transient cases of myocarditis, with a higher risk from the Moderna vaccine.

The F.D.A. notified Moderna on Friday that it would need more time to assess the vaccine’s safety and may not deliver a decision until January 2022, the company said in a statement on Sunday. The agency took roughly a month to authorize the Pfizer-BioNTech vaccine for children ages 12 to 15 years. That vaccine has been available to adolescents in the United States and Europe since May.

Even with the heightened risk, myocarditis as a result of the vaccine is rare, mild, and resolves quickly, noted Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia and a member of the F.D.A.’s vaccine advisory committee.

Covid-19 is much more likely to cause myocarditis, Dr. Offit noted, because the virus can infect and damage the lining of the heart. “That would be the decision point I would make for my child,” he said.

In studies from Israel and the United States, the incidence of heart problems among people who had received Pfizer-BioNTech or Moderna vaccine is highest in males aged 16 to 29 years. The risk appears to decline in children 12 to 15, and is expected to be even lower in younger children, Dr. Offit said.

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