Pfizer announced Monday that its COVID-19 vaccine is safe and effective in children aged 5 to 11 years old, and that it will seek US approval for this age group soon – a critical step toward starting vaccines for children.

Pfizer and its German partner BioNTech have already made the vaccination available to anybody aged 12 and up. However, with children returning to school and the extra-contagious delta variant producing a spike in pediatric infections, many parents are looking forward to immunizations 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, 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, followed shortly afterward with applications to European and British regulators.