The Meals and Drug Administration is reviewing studies suggesting the coronavirus vaccine made by Moderna could cause coronary heart issues in some adolescents, the corporate mentioned on Sunday.

Moderna requested authorization from the F.D.A. to be used of its vaccine in youngsters ages 12 to 17 years in June. The adolescents would obtain 100 micrograms of the vaccine — the identical dose given to adults 18 and above. However the company has not but made a ruling on the appliance, prompting hypothesis about causes for the delay.

In a press release on Sunday, Moderna mentioned the F.D.A. “requires extra time to guage current worldwide analyses of the danger of myocarditis after vaccination.”

The European Medicines Company authorized the vaccine to be used in adolescents in July. However since then, a number of European international locations have paused the vaccine’s use in folks 30 and youthful, citing considerations about myocarditis — an irritation of the guts muscle.

Moderna mentioned greater than 1.5 million adolescents worldwide have obtained its coronavirus vaccine, and the info to this point don’t counsel an elevated threat of myocarditis. However research from Israel and the US have linked each the Pfizer-BioNTech and Moderna vaccines to uncommon and transient circumstances of myocarditis, with a better threat from the Moderna vaccine.

The F.D.A. notified Moderna on Friday that it might want extra time to evaluate the vaccine’s security and will not ship a choice till January 2022, the corporate mentioned in a press release on Sunday. The company took roughly a month to authorize the Pfizer-BioNTech vaccine for youngsters ages 12 to fifteen years. That vaccine has been accessible to adolescents in the US and Europe since Could.

Even with the heightened threat, myocarditis because of the vaccine is uncommon, delicate, and resolves shortly, famous Dr. Paul Offit, director of the Vaccine Schooling Heart at Youngsters’s Hospital of Philadelphia and a member of the F.D.A.’s vaccine advisory committee.

Covid-19 is more likely to trigger myocarditis, Dr. Offit famous, as a result of the virus can infect and injury the liner of the guts. “That might be the choice level I’d make for my baby,” he mentioned.

In research from Israel and the US, the incidence of coronary heart issues amongst individuals who had obtained Pfizer-BioNTech or Moderna vaccine is highest in males aged 16 to 29 years. The danger seems to say no in youngsters 12 to fifteen, and is anticipated to be even decrease in youthful youngsters, Dr. Offit mentioned.

The F.D.A. in July requested Pfizer-BioNTech and Moderna to enroll extra youngsters of their medical trials with the intention to detect much less frequent uncomfortable side effects. Final week, after reviewing knowledge from a medical trial of the Pfizer-BioNTech vaccine in youngsters aged 5 by way of 11 years, the F.D.A. licensed the vaccine for that age group.

Outcomes from Pfizer’s vaccine trial in youngsters underneath 5 usually are not anticipated until the fourth quarter of this yr on the earliest. Final week, Moderna mentioned its vaccine produced a potent immune response in youngsters ages 6 by way of 11 who obtained half the grownup dose. The corporate plans to request authorization from the F.D.A. for the vaccine’s use on this age group.