Moderna is seeking emergency use authorization from the US Food and Drug Administration for its Covid-19 vaccine for children 6 months through 5 years of age, the company said Thursday.

"We believe mRNA-1273 will be able to safely protect these children against SARS-CoV-2, which is so important in our continued fight against COVID-19, and will be especially welcomed by parents and caregivers," Stéphane Bancel, chief executive officer of Moderna, said in a news release.

No Covid-19 vaccines have been authorized for children younger than 5 in the US -- about 18 million people -- and a timeline to potential authorization is not yet clear. Moderna officials have said the FDA is expected to move fast, and a Pfizer official suggested its vaccine for younger children could be available in June, if its authorized.

Dr. Peter Marks, director of the FDA's Center for Biologics Evaluation and Research, this week called vaccines for younger children "one of our highest priorities," but acknowledged the agency needed complete applications from vaccine manufacturers in order to finish its review.