Pfizer Inc. and partner BioNTech SE have said their COVID-19 vaccine was safe and produced strong antibody responses in children age 5 to 11 in a large-scale trial, findings that could pave the way for the start of vaccinations for grade-school kids within months.

The long-awaited results offer one of the first looks at how well a COVID-19 vaccine could work for younger children. Pressure to immunize kids has been on the climb in the U.S., where a new school year has started just as the delta variant is fueling a surge in cases.

In a trial with 2,268 participants, two shots of a 10 microgram dose — one-third of the adult shot — produced antibody levels comparable to those seen in a trial of 16- to 25-year-olds who got the adult dose, the companies said, with similar side effects.