The Food and Drug Administration on Monday authorized booster doses of Pfizer-BioNTech’s coronavirus vaccine for 12- to 15-year-olds, a group that became eligible for initial shots in May.

A booster dose “may help provide better protection against both the Delta and Omicron variants,” said Dr. Peter Marks, a top regulator who oversees the agency’s vaccines office. “In particular, the Omicron variant appears to be slightly more resistant to the antibody levels produced in response to the primary series doses from the current vaccines.”

Dr. Peter Marks, who oversees the agency’s division that regulates vaccines, said that the risk of myocarditis was substantially lower after a booster dose than after a second dose, citing U.S. safety monitoring data. The benefits of a third shot outweighed the potential risks, he said, because it may better protect individuals against both the Delta and Omicron variants.