Advisers to the Centers for Disease Control and Prevention are meeting on Wednesday to address reports of rare heart problems in young people immunized with the coronavirus vaccines made by Pfizer-BioNTech and Moderna.
The reports involve conditions called myocarditis, inflammation of the heart muscle; and pericarditis, inflammation of the membrane surrounding the heart. Most cases have been mild, with symptoms like fatigue, chest pain and disturbances in heart rhythm that quickly clear up. The agency is tracking nearly 800 reports, although not all have definitively been linked to the vaccines.
The C.D.C. advisers’ meeting comes as the Biden administration publicly acknowledges that it expects to fall short of its goal of getting 70 percent of Americans partly vaccinated by July 4. The shortfall, officials said on Tuesday, results in part from reluctance among younger Americans to be immunized.
Experts have said that the benefits of immunization far outweigh the risk of the possible problems, but they are expected to revisit that debate, particularly for adolescents and young adults.
More than half of the heart problems were reported in Americans ages 12 to 24, while that age group accounted for only 9 percent of the millions of doses administered. The numbers are higher than would be expected for those ages.
As of May 31, 216 people had experienced myocarditis or pericarditis after one dose of either vaccine, and 573 after the second dose. While most cases were mild, 15 patients remained in hospitals at that time. The second dose of the Pfizer-BioNTech vaccine was linked to about twice as many cases as the second dose of the vaccine made by Moderna.
“We look forward to more clarity regarding the potential risk of myocarditis after mRNA vaccines to increase vaccine confidence and vaccination rates,” said Dr. Yvonne Maldonado, chair of the Committee on Infectious Diseases at the American Academy of Pediatrics.
Recommendations from the C.D.C. advisers after Wednesday’s meeting may also influence decisions to immunize children younger than 12 when vaccines become available for that age group. Some experts have questioned whether the benefits to children outweigh the potential risks, given the low odds of serious illness in young children.
The C.D.C. strongly recommends Covid-19 vaccines for Americans ages 12 and older. The agency reported this month that the number of hospitalizations related to Covid-19 among adolescents in the United States was about three times higher than hospitalizations linked to influenza over three recent flu seasons.
As of June 10, nearly 17,000 children in 24 states had been hospitalized for Covid-19 and 330 children had died, according to data collected by the American Academy of Pediatrics.