The U.S. Food and Drug Administration on Friday authorized two COVID-19 vaccines for children under 5, opening the door to vaccinating millions of the country's youngest children once the Centers for Disease Control and Prevention agrees.

The FDA authorized Pfizer-BioNTech's COVID-19 vaccine for children aged 6 months to 4 years and Moderna Inc's shot for those 6 months to 17 years. Pfizer's is already authorized for those over the age of 5.

The vaccines could be rolled out to the under-5 age groups as early as next week, White House officials have said. The CDC needs to make its recommendations on how the shots should be administered before a vaccination campaign can begin in earnest.

"We will begin shipping millions of vaccine doses for kids to thousands of locations parents know and trust—including pediatricians’ offices, children’s hospitals, and pharmacies," Biden said in a statement on Friday.

"As doses are delivered, parents will be able to start scheduling vaccinations for their youngest kids as early as next week, with appointments ramping up over the coming days and weeks."

A panel of outside advisers began meeting on Friday to consider a recommendation to the CDC on the shots for those under 5 years old and will vote on Saturday, likely followed by the CDC itself greenlighting the recommendation.

While many parents in the United States are eager to vaccinate their children, it is unclear how strong demand will be for the shots. The Pfizer-BioNTech vaccine was authorized for children aged 5 to 11 in October, but only about 29% of that group is fully vaccinated so far, federal data shows.

COVID-19 is generally milder in children. Still, since March 2020 it has been the fifth leading cause of deaths in children aged 1-4 and the fourth leading cause of death in children younger than 1, according to the CDC.

"Although the number of deaths in children is small by adult standards, any death of a child is tragic and should be prevented if possible," FDA Commissioner Robert Califf said at a press conference on Friday. "By vaccinating our youngest children, we hope to prevent the most devastating consequences of COVID."

CVS Health Corp, Walmart Inc and Rite Aid Corp plan to provide COVID-19 vaccinations to young children in the United States if the vaccines are authorized, the companies said on Thursday.

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 hospitalizations and deaths when cases rise again.

The CDC advisers will meet again next week to consider whether to back the use of Moderna for older children, aged 6-17. There has been some concern about the rate of rare cases of heart inflammation in young men from the Moderna vaccine, and the advisers are expected to consider that data.

Moderna shares rose 5% while Pfizer shares were down 2% in afternoon trading.

(Reporting by Manas Mishra in Bengaluru; Editing by Sriraj Kalluvila, Peter Henderson, Mark Porter and Leslie Adler)