Pfizer reported on Friday that its vaccine was 90.7 percent effective in preventing symptomatic Covid-19 in children ages 5 to 11, according to clinical trial data.

The company submitted the information to the Food and Drug Administration, which was expected to release its own analysis of the data later in the day.

Children in the trial received a dose of 10 micrograms, smaller than the 30-microgram dose given to adults. The company said that the dosage was safe, and that trial participants had seen only mild side effects.

Of 2,268 children in the trial, twice as many were given the vaccine as received a placebo. Sixteen children who received the placebo got Covid-19, compared with three who received the vaccine, a result that translates to more than 90 percent efficacy.

The company released the data before a meeting next week at which expert advisers to the F.D.A. will decide whether to recommend that the agency authorize the vaccine for children in this age group. Federal regulators have already made the vaccine available for those 12 and older.

If the F.D.A. authorizes the vaccine for ages 5 to 11 — a move that could help protect more than 28 million people in the United States — the Centers for Disease Control and Prevention will then make recommendations to the agency next month on how the shots should be administered.

According to data collated by The New York Times, 66 percent of the U.S. population has received at least one dose of a Covid vaccine, while 57 percent are fully vaccinated.