The U.S. Food and Drug Administration last week authorized a booster of the Pfizer-BioNTech COVID-19 vaccine for young children.

Fully vaccinated children between the ages of 5 and 11 will now be eligible for a single booster dose. Pfizer is the only brand approved for the booster shots in younger children.

The FDA reported the third shot was safe and generated a significant immune response after studying trial results.

“While it has largely been the case that COVID-19 tends to be less severe in children than adults, the omicron wave has seen more kids getting sick with the disease and being hospitalized, and children may also experience longer term effects, even following initially mild disease,” FDA Commissioner Dr. Robert M. Califf said in a statement Tuesday.

Federal data shows 43.6% of eligible children between the ages of 5 and 17 have been fully vaccinated. Less than 30% of children between 5 and 11 are fully vaccinated.

However, 18.2 million children — 25.7 children overall — between 5 and 11 remain unvaccinated.

As COVID-19 cases are on the rise again with a 76% increase, pediatric hospital admission rates have also increased by 57% in the last month.

Nearly 13.2 million children have tested positive for the virus since the onset of the pandemic, and children represent about a fifth of all reported cases on record.

Children under the age of 5, about 18 million, are the only group not yet eligible for vaccination again the virus.