The U.S. Food and Drug Administration has authorized user of the COVID-19 vaccines from Pfizer and BioNTech, and from Moderna, for kids between 6 months and 5 years of age. The FDA’s decision follows a length review process, and the dosage for children under 5 is greatly reduced relative to those for older children and adults.

While Pfizer’s vaccine was previously authorized in the U.S. for people 5 and up, Moderna’s inoculation was limited to those aged 18 or above. The new authorization clears use of Moderna for children aged 6 months to 17 years.

This isn’t the final step before inoculation programs begin for the new age groups: The Centers for Disease Control will offer additional guidance and a recommendation, which is a step not strictly required, but usually followed, by doctors and pharmacists who perform the inoculations. Still, vaccinations for those under 5 in the U.S. could begin rolling out as soon as Monday.

The FDA’s decision is based on tests of more than 4,526 volunteer participants, while Moderna’s is based on a study involving over 6,300 children.