The agency authorised Pfizer-BioNTech’s vaccine for children aged six months to four years, and Moderna Inc’s shot for those six months to 17 years.

Pfizer’s is already authorised for those over the age of five.

While many parents in the US are eager to vaccinate their children, it is unclear how strong demand will be for the shots.

The Pfizer-BioNTech vaccine was authorised for children aged five to 11 in October, but only about 29% of that group is so far fully vaccinated, federal data shows.

The vaccines could be rolled out to the under-five age groups as early as next week, White House officials have said, although the Centers for Disease Control and Prevention still needs to make its recommendations on how the shots should be administered before the vaccination campaign can begin in earnest.

A panel of its outside advisers is meeting to vote on the recommendations today and tomorrow.

“Those trusted with the care of children can have confidence in the safety and effectiveness of these Covid-19 vaccines and can be assured that the agency was thorough in its evaluation of the data,” FDA commissioner Robert Califf said in a statement.

Public health officials and experts say that even though a large portion of small children were infected during the winter surge due to the Omicron variant of the coronavirus, natural immunity wanes over time and vaccinations should help prevent hospitalisations and deaths when cases rise again.

Moderna shares rose over 3% to US$125.16, while Pfizer was up nearly 1% at US$47.81 in morning trading.