COVID-19 vaccine
COVID-19 vaccineiStock

The Centers for Disease Control is investigating a small number of young adults and adolescents who may have experienced heart problems following a COVID-19 vaccine, though the agency stressed that it is unclear the vaccine is responsible, Fox News reported Saturday.

There have been "relatively few" reports of myocarditis and "most cases appear to be mild," but the COVID-19 Vaccine Safety Technical Work Group said it felt the potential issue should be communicated to providers.

The CDC noted that mRNA vaccines, which are made by Moderna and Pfizer-BioNTech, are potentially causing the problem.

Reports of myocarditis have been mostly in adolescents and young adults, are more common in males than females, typically occur after the second dose, and show up about four days after vaccination, according to Fox News.

The COVID-19 Vaccine Safety Technical Work Group discussed the issue during a meeting on May 17.

The FDA approved the use of Pfizer's vaccine for children as young as 12 earlier this month following a successful trial in which more than 2,000 US adolescent volunteers were given the shot.

In March, the drugmakers said the vaccine was found to be safe, effective and produced robust antibody responses in 12- to 15-year-olds in a clinical trial.

Pfizer has also begun testing its vaccine on younger children. The global study of 144 participants will also examine whether the vaccine can generate an immune response in children and determine the proper dosage for each age group in the trial: 6 months to 2 years; 2 years to 5 years; and 5 years to 11 years.

Moderna is also seeking approval of its vaccine for adolescents, saying that its vaccine has proven to be safe and effective in 12- to 17-year-olds.

There are about 1.5 million cases of myocarditis every year, which amounts to 10 to 20 cases per 100,000 persons, according to a study published last year in the medical journal StatPearls.