The U.S. Food and Drug Administration on Friday authorized two COVID-19 vaccines for children aged 5 and under, opening the door for vaccinating millions of the youngest American children.

The agency authorized Pfizer-BioNTech's vaccine for children aged 6 months to 4 years, and Moderna Inc's shot for those 6 months to 17 years. The Pfizer vaccine is already authorized for use in children and teens over the age of 5.

The vaccines could be rolled out for the under-5 age groups as early as next week, White House officials have said, and pharmacy chains have conveyed that they are ready to distribute the shots.

An advisory panel of the U.S. Centers for Disease Control and Prevention, which first needs to make its recommendation on the use of the shots, is scheduled to meet on Friday and Saturday.

While many American parents are eager to vaccinate their children, its unclear how strong the demand will be for the shots. The Pfizer/BioNTech vaccine was authorized for children ages 5 to 11 in October, but only about 29% of that group is fully vaccinated, according to federal data.

"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 hospitalizations and deaths when cases rise again.

The companies had presented data showing that there were no new safety concerns in that age group and the vaccines generated a strong immune response.

(Reporting by Manas Mishra in Bengaluru; Editing by Sriraj Kalluvila)