WASHINGTON The Food and Drug Administration on Monday authorized booster shots of the Pfizer-BioNTech coronavirus vaccine for 12- to 15-year-olds, part of a broader effort to expand protection as schools, airlines and businesses struggle with massive disruptions caused by a surging omicron variant.

The FDA also shortened to five months the time required between the second dose of the Pfizer-BioNTech vaccine and a booster shot; previously, the interval was six months.

In addition, it cleared third vaccine doses for some younger children with impaired immune systems. The moves are scheduled to be reviewed by the Centers for Disease Control and Prevention and its advisers this week, with CDC Director Rochelle Walensky expected to sign off as soon as Wednesday.

The changes came as the United States averaged more than 440,000 new coronavirus cases each day as of Monday, double the previous week, according to seven-day averages tracked by The Washington Post. The single-day total for Monday edged above 1 million cases, but most states reported data for multiple days because of the holiday weekend.

The number of patients hospitalized with confirmed or suspected COVID-19 is up 31% from last week, with about 1,500 Americans dying each day, a 50% increase since Dec.1.

Starbucks told its nearly 220,000 U.S. employees they must be fully vaccinated or submit to weekly testing. The workers must notify the company of their vaccination status by Jan. 10.

Congress’ attending physician warned lawmakers and their staff that the seven-day test-positivity rate at the Capitol increased from less than 1% to more than 13%. Brian P. Monahan urged as many people as possible to work remotely and to wear better masks — a KN95 mask or N95 mask.

“The daily case rates will increase even more substantially in the coming weeks,” Monahan wrote. “These cases represent both a rising rate of ‘breakthrough infections’ among mostly previously vaccinated individuals and several unvaccinated individuals.”

For increasingly anxious parents, the FDA authorization of Pfizer-BioNTech booster shots for 12- to 15-year-olds came as a relief. Some health experts lauded the move, but others criticized it, saying the initial two-shot series of shots provided adequate protection against severe disease. They questioned whether healthy children should be given an extra shot of a vaccine that has been linked to a rare cardiac side effect called myocarditis.

On a call with reporters explaining their decisions, FDA officials said the agency broadened access to boosters because data from real-world experience and laboratory tests indicate the shots significantly strengthen protection — especially against the omicron variant — while posing minimal risk.

The officials cited Israeli data involving more than 6,300 12- to 15-year-olds that showed no new safety issues among those who received a third dose of the Pfizer-BioNTech vaccine. And they said there were no new cases of heart-related complications.

The FDA also said someone who got two shots of the Pfizer-BioNTech vaccine can get a third shot of that vaccine or another one after five months, rather than six months.

The intervals for the other vaccines are unchanged. People who got the initial two-shot Moderna series are supposed to wait at least six months to get a booster, and those who received the Johnson & Johnson vaccine are supposed to wait two months.