CDC investigating cases of heart inflammation in teens, young adults who got two-shot COVID vaccine. Here's what we know.

Health officials are looking into reports of heart problems occurring in young adults and teenagers who have received the mRNA COVID-19 vaccines, according to a vaccine safety group with the Centers for Disease Control and Prevention.

In a May 17 meeting, the group presented reports of the heart condition, called myocarditis, to the CDC's Advisory Committee on Immunization Practices from safety data collected by the Department of Defense, the Vaccine Adverse Event Reporting System (VAERS), and Vaccine Safety Datalink (VSD).

The news comes a few weeks after the Food and Drug Administration authorized Pfizer’s COVID-19 vaccine for minors 12 and older. Moderna's vaccine is currently authorized for people 18 and older. The safety group did not specify which vaccine was given in these cases.

“It’s terrific that things are being transparent. … It shows the surveillance systems are working,” said Dr. Lawrence Kleinman, professor and vice chair of the department of pediatrics at Rutgers Robert Wood Johnson Medical School.

While little is known, here's what health experts say about these cases.

What we know

The vaccine safety group says the “relatively few” reports of myocarditis “appear to be mild” and are below the expected baseline rates.

Among the cases, the heart condition appeared in adolescents and young adults, and more often in men than women. Symptoms typically appeared within four days after the second dose. Follow-up on the cases is ongoing, the work group said.

"Information about this potential adverse event should be provided to clinicians to enhance early recognition and appropriate management of persons who develop myocarditis symptoms following vaccination," the work group concluded.

What is myocarditis and what are the symptoms?

Myocarditis is inflammation in the heart muscle that can affect the heart’s electrical system, reducing its ability to pump, according to the Mayo Clinic.

Signs and symptoms of myocarditis in children may include fever, fainting, breathing difficulties, rapid breathing and rapid or abnormal heart rhythms, called arrhythmias.

“It’s not common (in children) but neither is it a rare thing where its presence can be said to be definitively associated with the vaccine,” Kleinman said.

Myocarditis can be caused by a whole host of viruses, including COVID-19, said Dr. Federico Laham, medical director for Orlando Health Arnold Palmer Hospital for Children Infectious Diseases.

During the pandemic, some cases of myocarditis appeared in children with Multisystem Inflammatory Syndrome in Children, or MIS-C, which is another serious condition that occurs after COVID-19 infection where some organs and tissues become severely inflamed.

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Health experts say it’s possible the few cases reported by the vaccine safety group may not be related to the vaccine at all. The myocarditis could have been caused by an asymptotic infection of SARS-CoV-2 or any other virus seasonally more present in the spring and summer.

Last year, pediatricians saw a decrease in myocarditis during the spring and summer as children follow public health guidance to wear masks and socially distance, Laham said.

“It’s logical that we’re going to see a rebound (this year),” he said.

What comes next?

Health experts say it’s unlikely the CDC will recommend a pause of the mRNA vaccines as it did with the Johnson & Johnson vaccine when the agency was investigating possibly associated rare blood clots.

Most of the vaccinations administered in the U.S. are mRNA vaccines, with nearly 155 million doses of Pfizer and 122 million doses of Moderna given to Americans as of May 24, according to the CDC.

“We don’t have the luxury of being able to take a full time out because the dynamic of COVID spread is still very real and children remain a large unvaccinated reservoir,” Kleinman said.

Laham agreed.

“The cases have been very few and I don’t think there’s any reason to stop and change the course of the vaccine recommendations,” he said.

Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

This article originally appeared on USA TODAY: COVID-19 vaccine heart problems in teens, young adults: What we know