Pfizer Inc and BioNTech SE said on Wednesday their coronavirus (COVID-19) vaccine was 100 percent effective and produced robust antibody responses in 12- to 15-year olds.

The vaccine was 100% effective in protecting against symptomatic disease, said the companies, who tested the drug on more than 2,260 children during phase three trial.

Researchers also didn’t find any safety concerns, Pfizer and BioNTech said.

Given the results, Pfizer said it would ask U.S. health regulators in the coming weeks to expand use of the shots to 12- to 15-year-olds.

The vaccine was well tolerated, with side effects in line with those seen among those aged 16 to 25 in the adult trial. It did not list the side effects for the younger group, but the adult trial’s side effects generally were mild to moderate and included injection-site pain, headaches, fever and fatigue.

The companies also studied a subset of teens to measure the level of virus-neutralizing antibodies a month after the second dose and found it was comparable to study participants aged 16 to 25 in the pivotal trial in adults.

Last week, the companies gave the first vaccine doses in a series of trials testing the vaccine in younger children, that will eventually go to those as young as 6 months of age.