Some 789 Americans have reported heart inflammation following their mRNA COVID-19 vaccinations, and 275 of those cases are in ages 16-24, the Centers for Disease Control and Prevention said Thursday.
To date, 143 million Americans have received the vaccine. The cases of inflammation, known as myocarditis in young Americans "exceeded the expected amount," said Dr. Tom Shimabukuro, with the CDC's Immunization Safety Office, in a Thursday briefing. The CDC had put the expected rate between 10 and 102 cases.
Given that nearly half of all American adults have received at least one dose of a COVID-19 vaccine, the occurrence remains a rare event. But it warrants following, Shimabukuro said. CDC officials also said they plan to hold an "emergency meeting" June 18 to discuss the cases.
"It's still early. ... We are still gathering information, and I believe we will ultimately have sufficient information to answer questions. We will have updated information next Friday that will put it in the context of benefit and risk," he said.
The findings, he added, are "consistent with surveillance data that has emerged from Israel, as well as case series reports and the Department of Defense."
According to the briefing, the majority of myocarditis cases were reported in men, in individuals who received a second vaccination, and in those who received the Pfizer vaccine, which Shimabukuro said has been used in more Americans than the Moderna vaccine.
The median time to the onset of inflammation symptoms is two to three days, he added.
The briefing was conducted as part of a review to discuss safety issues of the COVID-19 vaccines in pediatric patients.
The CDC began looking into cases of myocarditis in a small number of Americans vaccinated against COVID-19 in late May.
The move followed an announcement in late April by Israel's Health Ministry that it was reviewing cases of myocarditis in young people after they received the Pfizer vaccine and an April 24 report by Military.com of 14 cases being tracked within the DoD health system. The DoD now has at least 17 cases.
During Thursday's briefing, Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, cautioned that his organization still doesn't "know whether this is truly related to the vaccine."
Myocarditis can be caused by a virus, and cases have been linked to COVID-19. But several of the individuals reported to the CDC tested negative for COVID-19 at the time of their diagnosis.
According to the CDC, 81% of the reported cases that were reviewed have made a full recovery. As of May 31, 15 people remain hospitalized, with three in intensive care.
Health officials maintain that the risk of contracting a severe case of COVID-19 currently outweighs any risks associated with the vaccine.
-- Patricia Kime can be reached at Patricia.Kime@Monster.com. Follow her on Twitter @patriciakime.