Children between six months and four years old can receive the Pfizer-BioNTech SE shot at least two months after completing their primary series of vaccinations, the US Food and Drug Administration said Tuesday.

Kids who have already had a Pfizer-BioNTech bivalent vaccine aren’t approved to get jabbed again, because they’re adequately protected against the most serious Covid-19 complications, the FDA said. 

The authorization closes an inoculation gap for young children who were able to receive a series of three monovalent Pfizer shots but were ineligible to then get the company’s bivalent booster. The bivalent shot is designed to protect against two omicron variants, called BA4 and BA5.

Starting in December, the FDA allowed infants and children to receive the bivalent shot as the third dose in their primary series of Covid vaccinations. The FDA also then authorized the use of Moderna Inc.’s mRNA bivalent vaccines for the age group.

Booster uptake in all age groups has dropped, with only 16% of Americans getting the latest round of shots targeting omicron.