The U.S. Food and Drug Administration (FDA) requires more time to decide whether to approve the use of the Moderna COVID-19 vaccine in children aged between 12 and 17, according to the company.

The FDA has extended the timeline so it can look into reports of a rare side effect called myocarditis (inflammation of the heart muscle) in those who have received the shot.

The Massachusetts-based pharma company said the FDA informed it of the delay on Friday.

Moderna said in a statement, “The safety of vaccine recipients is of paramount importance to Moderna. The Company is fully committed to working closely with the FDA to support their review and is grateful to the FDA for their diligence.”

The agency’s review of Moderna’s application for an Emergency Use Authorization (EUA) of its COVID vaccine in teenagers may not be completed before January. The company requested the FDA’s authorization for use in adolescents in June.

Moderna went on to say that the FDA is reviewing “recent international analyses” of the possible side effect.

A recent Swedish study has shown that there is a slightly increased risk of heart muscle inflammation, promoting four nations to stop distributing the vaccine to young men and boys.

The European Medicines Agency (EMA) had previously approved Moderna’s vaccine for use in children aged between 12 and 17.

However, the company said it did not yet have access to the recent international analyses, estimating that over 1.5 million adolescents had received its jab and said there have been no reports of myocarditis in people younger than 18.

Not only Moderna but also Pfizer-BioNTech COVID-19 vaccine has shown to produce myocarditis as a rare side effect. However, it has been found that most viral infections, including COVID, can cause myocarditis too. Also, most children and adolescents who experience this rare side effect recover.

Recently, the FDA approved the use of the Pfizer-BioNTech COVID-19 vaccine in children aged between 5 and 11. The FDA’s advisory panel said the benefits of protecting kids against COVID-19 outweigh the possible increased risk of myocarditis.

The FDA has already granted EUA to Moderna for the use of its COVID-19 vaccine in adults.

On Sunday, the company said it would delay applying for EUA for its vaccine to be given to children aged between 6 and 11 until the FDA completely reviews it.

The article appeared on NPR Health.