C.D.C. Investigating Cases of Heart Inflammation Following Immunization

Federal officials are reviewing nearly 800 cases of rare heart problems after immunization with Pfizer-BioNTech and Moderna’s coronavirus vaccines, according to the data presented at a vaccine safety meeting Thursday.

It is likely that not all cases are reviewed or related to vaccines, and experts believe that the benefits of vaccination far outweigh the risk of these rare complications. But the reports have worried some researchers. More than half of heart problems were reported in people ages 12 to 24, while the same age group accounted for only 9 percent of the millions of doses given.

“We clearly have an imbalance,” said Dr. Tom Shimabukuro, a vaccine expert from the Centers for Disease Control and Prevention, who presented the data. The agency’s advisors will meet on June 18 to investigate the possible links to the complications: myocarditis, inflammation of the heart muscle and pericarditis, inflammation of the membrane surrounding the heart.

About two thirds of the cases involved young men with an average age of 30 years. The numbers are higher than expected for this age group, officials said, but have not yet been definitively linked to the vaccines.

As of May 31, 216 people had developed myocarditis or pericarditis after a dose of either vaccine and 573 after the second dose. Most of the cases were mild, but 15 patients remain in hospitals. The second dose of Pfizer BioNTech vaccine was associated with approximately twice as many cases as the second dose of Moderna’s vaccine.

There were 79 reported cases of heart problems in the 16- or 17-year-olds, compared to a maximum of 19 cases expected for this group. And in the group of adolescents aged 18 to 24, there were 196 cases, compared to an expected maximum of 83.

But the true incidence could be lower, said Dr. Shimabukuro. Vaccinations of younger adolescents only started last month and limited data are available, especially for this age group.

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