Kid-size doses of Pfizer’s coronavirus vaccine appear safe and almost 91 per cent effective at preventing symptomatic infections in 5 to 11-year-olds according to study details released Friday, as the US considers opening vaccinations to that age group.

The shots could begin in early November — with the first children in line fully protected by Christmas — if regulators give the go-ahead.

Details of Pfizer’s study were posted online. The Food and Drug Administration (FDA) was expected to post its independent review of the company’s safety and effectiveness data later in the day.

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Advisers to the FDA will publicly debate the evidence next week. If the agency ultimately authorises the shots, the Centers for Disease Control and Prevention will make the final decision on who should receive them.

Full-strength Pfizer shots are already authorised for anyone 12 or older, but pediatricians and many parents are waiting for something that can protect younger children from the extra-contagious delta variant and help keep kids in school.

More than 25,000 pediatricians and primary care providers already have signed up to get the shots for the kids.

A Pfizer study tracked 2,268 kids in that age group who got two shots three weeks apart of either a placebo or the low-dose vaccine. Each dose was one-third the amount given to teens and adults.

Researchers calculated the low-dose vaccine was nearly 91 per cent effective, based on 16 virus cases in youngsters given dummy shots versus three cases among vaccinated children. There were no severe illnesses reported among any of the youngsters, but the vaccinated ones had much milder symptoms than their unvaccinated counterparts.

Pfizer’s study of younger kids found the low-dose shots proved safe, with similar or fewer temporary side effects such as sore arms, fever or achiness that teens experience.

The study isn’t large enough to detect any extremely rare side effects, such as the heart inflammation that occasionally occurs after the second dose, mostly in young men.

While children run a lower risk of severe illness or death than older people, Covid-19 has killed more than 630 Americans 18 and under, according to the CDC. Nearly 6.2 million children have been infected with the coronavirus, more than 1.1 million in the last six weeks as the delta mutant surged, the American Academy of Pediatrics says.

Moderna also is studying its vaccine shots in elementary school-age youngsters. Pfizer and Moderna are studying even younger children as well, down to 6-month-olds. Results are expected later in the year.