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.

“We are ready to execute, pending CDC’s decision. And starting the week of November 8th, our vaccination program for kids ages 5 through 11 will be running at full strength,” Zients told reporters at a briefing.

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 visitvaccines.gov and filter locations offering the vaccine for the children, Zients said.

“The whole plan is based on Pfizer vaccines,” he said.

Moderna Inc said on Sunday it would delay filing its request for an emergency use authorization for a half-strength 50-microgram dose of the vaccine for children ages6 to 11.

Shares in Moderna fell 2.3%, or $8.04, to $337.17 on Monday while Pfizer shares were off 10 cents at $43.64.

At the end of last week, the seven-day average number of coronavirus cases dropped 3% to around 69,000 daily cases, the average hospitalization rate fell 10% to around 5,100 cases, and the daily deaths average fell 10% to around 1,100, CDC DirectorDr. Rochelle Walensky said at the same briefing.

U.S. Chief Medical Advisor Dr. Anthony Fauci said it was “very likely” everyone would be able to get a vaccine booster shot “within a reasonable amount of time.”

Currently the CDC recommendations for boosters cover specific categories of people.