The Centers for Disease Control and Prevention is investigating some reports of heart problems in teens and young adults after receiving the COVID vaccine.
The agency said the "relatively few reports of myocarditis" primarily were reported following the second dose of the vaccine and most often occurred in males, according to the CDC's COVID-19 Vaccine Safety Technical Work Group, as reported by The New York Times.
Myocarditis is a condition that causes inflammation of the heart muscle, weakening the heart, which makes it work harder to circulate blood and oxygen through the body, according to the Myocarditis Foundation.
About 3.1 cases of myocarditis were diagnosed in 2017, the foundation said. Symptoms can include fatigue and chest pain as well as heart palpitations.
The CDC's report goes on to say that safety data of the heart condition cases seemed to have occurred predominately in adolescents and young adults, typically within four days after vaccination. The cases appeared to be mild, but follow-up of the cases is ongoing, according to the agency.
The FDA has approved the Pfizer COVID vaccine for use in children as young as 12 years old. Both the Moderna and Johnson & Johnson vaccines are approved for use in individuals aged 18 and older.
In its report, CDC said, "Within CDC safety monitoring systems, rates of myocarditis reports in the window following COVID-19 vaccination have not differed from expected baseline rates. However, VaST members felt that information about reports of myocarditis should be communicated to providers."
More detailed information on the cases was not provided by the agency, but the CDC's review is still in its early stages. No evidence to suggest that the COVID vaccine is linked to the heart condition reports in teens or young adults has been determined to date.
Dr. Yvonne Maldonado, chair of the American Academy of Pediatrics's Committee on Infectious Diseases, told the Times, "We look forward to seeing more data about these cases, so we can better understand if they are related to the vaccine or if they are coincidental. Meanwhile, it's important for pediatricians and other clinicians to report any health concerns that arise after vaccination."
About 300 children have died of COVID-19 in the U.S. as of May 13, according to the American Academy of Pediatrics.
As of Monday, over 130 million people had been fully vaccinated against COVID-19, representing 39.2% of the U.S. population. About 4.5 million people vaccinated were aged 12 to 18, the Times said.