NEW YORK (AP) — Pfizer said Monday its COVID-19 vaccine works for children ages 5 to 11 and that it will seek U.S. authorization for this age group soon — a key step toward beginning vaccinations for youngsters.

The vaccine made by Pfizer and its German partner BioNTech already is available for anyone 12 and older. But with kids now back in school and the extra-contagious delta variant causing a huge jump in pediatric infections, many parents are anxiously awaiting vaccinations for their younger children.

For elementary school-aged kids, Pfizer tested a much lower dose — a third of the amount that’s in each shot given now. Yet after their second dose, children ages 5 to 11 developed coronavirus-fighting antibody levels just as strong as teenagers and young adults getting the regular-strength shots, Dr. Bill Gruber, a Pfizer senior vice president, told The Associated Press.

The kid dosage also proved safe, with similar or fewer temporary side effects — such as sore arms, fever or achiness — that teens experience, he said.

“I think we really hit the sweet spot,” said Gruber, who’s also a pediatrician.

Gruber said the companies aim to apply to the Food and Drug Administration by the end of the month for emergency use in this age group.