By Ahmed Aboulenein and Alexandra Alper

WASHINGTON (Reuters) -The United States is rolling out Pfizer/BioNTech COVID-19 vaccines for children aged 5 to 11 this week, but most of the 15 million shots being shipped initially are unlikely to be available before next week, the White House said on Monday.

Millions of doses specifically formulated for children of that age group will start arriving at distribution centers over the next few days, White House coronavirus response coordinator Jeff Zients said, and the federal government has purchased enough supply for all eligible 28 million children.

“The whole plan is based on Pfizer vaccines,” Zients told reporters at a briefing. “So the bottom line is there’s plenty of supply of the Pfizer vaccine and we look forward to parents having the opportunity to vaccinate their kids.”

The U.S. Food and Drug Administration on Friday authorized the Pfizer Inc and BioNTech SE coronavirus vaccine for children aged 5 to 11 years, making it the first COVID-19 shot for young children in the United States.

The U.S. Centers for Disease Control and Prevention still needs to advise on how the shot should be administered, which will be decided after a group of outside advisers discuss the plan on Tuesday.

Following the CDC’s decision, parents will be able to visit vaccines.gov and filter locations offering the vaccine for the children, Zients said.

(Reporting by Ahmed Aboulenein and Alexandra Alper; Additional reporting by Susan Heavey in Washington and Michael Erman in New Jersey; Editing by Alison Williams)