Masks will again be required indoors in D.C. beginning Saturday, Mayor Muriel E. Bowser ordered, in a reversal of recent policy driven by new federal guidelines that recommend indoor masking in areas where coronavirus transmission is high.

The new requirement, which Bowser (D) announced Thursday, will apply to vaccinated and unvaccinated people over the age of 2.

This week, the Centers for Disease Control and Prevention announced a new approach, asking people in localities with more than 50 new cases per 100,000 residents per week — including the District, where case rates have risen sharply in recent weeks — to again wear masks indoors. Bowser said Thursday that she would go further and mandate it.

“I know D.C. residents have been very closely following the public health guidelines and they will embrace this,” she said at a news conference.

But many residents’ initial response was disappointment.

Tricia Davern, 22, said that she had been enjoying seeing friends this summer after a long year of shutdowns and online schooling.

“It’s hard to hear, especially when we got our hopes up,” Davern said as she walked out of an Eastern Market coffee shop Thursday afternoon. “We waited so long for the vaccine.”

What she will miss most with indoor masking, she said, is seeing people’s smiles.

The governors of Maryland and Virginia said they would not follow suit on masking. Both states lifted their masking mandates in May.

Michael Ricci, a spokesman for Maryland Gov. Larry Hogan (R), said in an email that “no new statewide mask mandate is under discussion.”

Maryland recorded 505 new coronavirus cases Thursday — the highest since the end of May. The state is experiencing a continued uptick, largely driven by the highly contagious delta variant.

Virginia Gov. Ralph Northam (D) tweeted Thursday, “All Virginians should consider wearing a mask in public indoor settings.” He cited the new CDC guidelines, then wrote, “This is not a requirement, but a recommendation.”

As of Thursday, Virginia’s new daily case rate for the week was slightly higher than the District’s and Maryland’s was slightly lower.

For many months of the pandemic, D.C. had one of the strictest mask mandates in the nation, requiring masks indoors and outdoors whenever one person came near another for more than a “fleeting” amount of time.

Bowser stopped requiring masks in many settings for vaccinated people in May and all residents in June, though the city continued mandating masks on public transit and in schools and government buildings.

The mayor said she has the power to reissue the requirement while the city remains in a state of emergency, though she allowed the broader public health emergency — which for months gave her the power to shut down businesses and other restrictions — to expire over the weekend.

Her order, which her staff said will be published Friday, will allow an exception for eating indoors in restaurants but not for exercising in a gym or working inside an office building, Bowser and Health Director LaQuandra Nesbitt said.

For private gatherings in people’s homes, Nesbitt recommended considering masks if attendees are particularly vulnerable.

Bowser has pushed for downtown office workers to return to their desks and said she hoped the requirement that they now work masked will not deter them.

“We continue to tell people to come to their offices and that we’re open,” she said.

While D.C.’s case rate has quadrupled recently, the new case rate, about 58 per 100,000 residents per week, is far lower than what it was during the worst of the pandemic. The delta variant plaguing much of the country has been scarcely detected in the District, and as cases among vaccinated people are generally not severe, the city’s hospitals are not overwhelmed by covid-19 patients.

Nevertheless, Nesbitt said the prospect of the delta variant encroaching in D.C. as it has in neighboring states was one of the main motivators for her to recommend restoring the mask requirement.

Bowser said she hopes the mask mandate will curb the surging case numbers enough that she will not have to bring back other restrictions that she dropped in May and June, such as social distancing requirements and capacity limits on businesses.

She would not offer a prediction on how long the new mask mandate will remain in place.

The fastest way to quash the spread of the virus, she emphasized again, is to get vaccinated. More than 70 percent of the District’s population has received at least one vaccine dose, but inoculation rates are far lower east of the Anacostia than in other neighborhoods.

Bowser said Thursday that she is in the process of negotiating rules on vaccination for city employees, who have already returned to work in person, with public employee unions.

Thursday’s announcement gave business owners until Saturday morning to change their signage and policies to reflect the city’s new rules.

At Agua 301, a Mexican restaurant in Navy Yard, owner Stephen Briggs said he welcomes Bowser’s action. He hopes it will slow the virus before it becomes so widespread that it could force restaurants to close again.

“We should get ahead of this before it causes more financial pains for everyone,” Briggs said as customers chatted around a high-top table over drinks. Only one wore a mask, pulled down below her chin.

Peter Kim and Jessica Choi strolled by hand in hand outside, both wearing masks even though they were outdoors.

They agreed that the mask mandate was the right thing to do given the rising number of cases and looming threat of the delta variant.

“It’s our civic duty, just to be able to keep ourselves safe and everyone else safe,” Choi said.

Ovetta Wiggins contributed to this report.