D.C. Mayor Muriel E. Bowser (D) on Monday reimposed the city’s indoor mask mandate and announced a stricter vaccination mandate for D.C. government workers — measures intended to confront a surge in coronavirus caseloads and the rise of the highly transmissible omicron variant.

The city will again legally require masks in most indoor public places, such as gyms, churches and grocery stores, beginning at 6 a.m. Tuesday.

Bowser’s announcement comes just over a month after she said the city would greatly relax the indoor mask mandate that had been in place since July, asserting at the time that vaccines were effective and preventing many people from requiring hospitalization. About two weeks later, as the new omicron variant fueled anxiety about the virus, the city’s health department issued a mask “advisory” that strongly recommended — but did not legally require — unvaccinated and vaccinated people wear masks in all indoor settings.

On Monday, Bowser said the mask mandate would last until Jan. 31, placing D.C. among the most restrictive local jurisdictions along with Montgomery County and Prince George’s County, which also have indoor masking requirements. There is no such mandate in Virginia, although the state health department recommends their use in areas where the spread of the virus is substantial or high.

Asked if she was considering further restrictions — like vaccine requirements for patrons at certain indoor venues such as restaurants, as New York City and Los Angeles have implemented — Bowser said yes, but added that no decision was imminent.

Bowser also declared a state of emergency that she said would allow for more efficient government operations. And she said the District will lengthen D.C. Public Schools students’ holiday break by two days, allowing time for them to pick up free rapid antigen tests, which the city will make available to students on Jan. 3 and 4. They are recommended, but not required, for all students before they return to class on Jan. 5.

The city will also distribute free rapid antigen tests for the first time at eight public libraries, starting Wednesday.

Speaking about the city’s residents and businesses who in the past months have seen the rules on masking change multiple times, Bowser said, “I think we’re all tired of it. I’m tired of it, too. But we have to respond to what’s happening in our city and what’s happening in our nation.”

New coronavirus cases in the District have risen sharply in December. The seven-day average of new cases per 100,000 people was 51.01 on Friday compared to 10.9 at the beginning of the month; the seven-day average of new hospitalizations has grown from 87 on Dec. 1 to 178 on Sunday — the highest rate of hospitalizations since May.

On Thursday and Friday, the most recent days that the city reported the tally of coronavirus cases, the District broke the record for most cases reported on a single day throughout the pandemic — two days in a row.

In Maryland, where there has been a blackout for the past two weeks because of a cyberattack, data was released Monday that gave the first glimpse of the spread of the virus in the state.

The state reported a seven-day daily positivity rate of 10.27 as of Friday, the highest in the region. The last time data was available, the seven-day rate was 5.43 percent. The state’s dashboard has not been fully updated.

For weeks, health officials have been operating without a real sense of the spread of the virus because of the cyberattack. One of the few metrics that has been updated the past two weeks is hospitalizations. On Monday the state reported 1,345 in Maryland, the highest it has been since early February. The surge has resulted in hospitals taking emergency measures, including canceling elective surgeries.

Gov. Larry Hogan (R), who announced Monday that he tested positive for the coronavirus, has said he has no plans on imposing new restrictions even as hospitals are expected in the coming weeks to experience their “worst surge” of the pandemic.

D.C.'s health department doesn’t yet have the data to attribute its surge in cases to the new omicron variant. Just 17 cases of omicron have been detected in the District, according to D.C. Health’s emergency response leader Patrick Ashley. But sequencing to determine which variant a patient has been infected with lags behind the initial testing that determines whether a test is positive or negative — and health officials warned Monday that the presence of omicron in the city will likely become more apparent in weeks to come.

Even as residents notice long lines at public and private testing sites, with a tremendous increase in demand for tests both because more people know they have been exposed to the virus and because they want to get tested before traveling for Christmas, Ashley said the average test turnaround time in D.C. remains just 1½ days.

When Bowser lifted her mask requirement in November, 10 of the 13 members of the D.C. Council called on her to reverse her decision, arguing that it was poorly timed ahead of winter holiday travel and when many children were not fully vaccinated.

Asked if she regretted her choice to end the mandate in November only to bring it back now, Bowser said Monday, “I don’t regret evolving with the virus.”

Bowser also said the District will soon require the city’s 37,000 employees to be fully vaccinated, including booster shots. In August, Bowser announced that all city employees and contractors would be required to get vaccinated, with an option for weekly testing in hopes that it would boost vaccination rates. But that test-out option is no more.

Officials said they still needed to partner with labor unions on the timing and specifics of the new requirement.

D.C. City Administrator Kevin Donahue provided an update Monday on religious exemption requests from D.C. government workers, which were largely submitted by workers who did not have the option for weekly testing, like certain health and school-based workers and D.C. Fire & Emergency Medical Services Department employees.

So far, there have been 866 religious exemptions and 75 medical exemption requests from government workers, he said. Of the religious exemption requests, 149 have been denied and one has been approved, Donahue said. Eight of the medical exemption requests have been approved, while 13 have been denied, he added. Decisions on the remainder are pending.

Donahue said that as the city expands the requirement without a test-out option, he expects more workers to request exemptions. Thus far, he added, 57 government workers have been suspended for failing to comply with the mandate, and 505 have received a written reprimand that they are out of compliance.

Starting Wednesday, rapid antigen coronavirus tests will be available to D.C. residents at eight public libraries, one in each ward. Residents will need to show valid D.C. identification or a piece of mail showing their D.C. address to receive the tests.

Ashley, the health department emergency response leader, said the city has ordered more than 1 million of the rapid tests, but has only received 42,000 so far. Each library will receive 2,000 tests daily, and residents will be allowed to take home four per person per day.

About 100,000 of the million tests that the city has ordered will go to the public school system, allowing every student and staff member to pick up a test kit from a public school building before returning from winter break.

School officials have said that coronavirus infection rates increased in schools after the Thanksgiving break. The city has moved nine schools to virtual instruction for the rest of the week before the holiday break: Whittier Elementary, McKinley Tech High School, Turner Elementary, Bard High School Early College, Beers Elementary, Boone Elementary, Miner Elementary, Stuart-Hobson Middle School and Takoma Elementary.

Other schools across the city have been prepping for another post-winter break covid-19 surge, and some will take a stricter approach than D.C. public schools’ test-recommended-but-optional approach.

KIPP DC, the city’s largest charter network, changed its plans last week: Now students will be returning to virtual instruction and learning asynchronously on Jan. 3.

All of the staff and students at KIPP DC must report to the school and get tested for the coronavirus. Students will return in staggered arrival times Jan. 4, and only staff and students with a verified negative rapid test will be admitted onto campus.

Nicole Asbury and Ovetta Wiggins contributed to this report.