By CBSBoston.com Staff

CAMBRIDGE (CBS) — The FDA plans to put a new warning on the Moderna coronavirus vaccine, made by a Cambridge biotech company, and the Pfizer vaccines. Researchers at the Centers For Disease Control found a “likely association” between the shots and rare cases of heart inflammation in young people, though health experts say the benefits of the vaccines still outweigh the risk.

The CDC is tracking more than 1,200 cases of myocarditis and pericarditis. Most of the cases happened after the second dose of the mRNA vaccines, and 65% were linked to Pfizer. The vast share of cases occurred in males 24 years old or younger.

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Doctors and researchers say they still strongly recommend all Americans 12 and older get the vaccine, as the heart problems are uncommon and in most cases very mild.

There are concerns that with fewer people getting vaccinated, the Delta variant could soon be the dominant strain, leading to a spike in cases and more deadly mutations.

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“The variants are just getting more and more powerful,” said Dr. Peter Chin Hong, an infectious disease expert at the University of California San Francisco. “Every two weeks, it’s making a mutation that could potentially be even worse than the last one.”

Dr. Yvonne Maldonado is a pediatric infectious disease expert at Stanford University.

“The bottom line for parents. . . I have three children myself, they’ve all been vaccinated. We would still elect to get the vaccine,” she said.

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The CDC says most patients with this heart inflammation responded well to treatment and rest and felt better quickly. Health experts are reminding people who choose not to get vaccinated that the virus itself can also cause health problems.

CBSBoston.com Staff