The omicron variant has surfaced in the Washington region, sparking renewed calls for mitigation from officials working to tamp down fears while bracing for the potential threat the latest coronavirus strain may pose.

Maryland Gov. Larry Hogan (R) said three cases were detected in residents who live in the Baltimore metro area.

“We urge Marylanders to continue taking precautions to keep themselves and their loved ones safe,” Hogan tweeted on Friday afternoon.

The cases are among the first to be detected in the United States. California Gov. Gavin Newsom (D) announced the first case in the country on Wednesday, which was swiftly followed by news of cases detected in New York, Colorado, Minnesota and Hawaii.

Two of the Maryland cases are from one household, including one person who was vaccinated and recently traveled to South Africa. The second person was unvaccinated and had close contact with the traveler. The third case, which involves a vaccinated person, is unrelated to the other two; officials said that case so far does not appear to be connected to travel.

None of the residents are hospitalized.

A preliminary study of the latest variant published this week in South Africa, where the strain was first detected late last month, found that omicron is at least three times as likely to cause reinfection than previous coronavirus variants. Researchers say the reinfection rate helps to explain the spread of the virus.

The study, which has not been peer-reviewed, did not address the level of protection vaccines provide against the latest variant. Hogan on Friday implored residents to get a shot and asked those already vaccinated to get a booster.

State and local health officials underscored the importance of mitigation 20 months into a pandemic that has killed more than 5.2 million people worldwide.

“The good news is that we know what we need to do to prevent the spread of the Omicron variant,” Nilesh Kalyanaraman, the health officer in Anne Arundel County, said in a statement. “It’s the same as what we do now. Get vaccinated, wear your mask in public settings, and get tested if you have symptoms.”

Across the Washington region, there has been an ever-shifting patchwork of different precautions.

Prince George’s County and Baltimore City have kept indoor mask mandates in place since the summer. Montgomery County, the region’s most-vaccinated jurisdiction, lifted its mask mandate in October, then reinstated it three weeks later when case rates ticked up.

Most of Northern Virginia has recommended but not mandated face coverings since the summer, and D.C. Mayor Muriel E. Bowser (D) on Thursday urged residents to mask up after easing masking requirements last week.

In the face of fluctuating requirements, many restaurants and shops have opted to continue asking patrons to mask up indoors unless they are eating.

Coronavirus cases have been rising in D.C., Maryland and Virginia since mid-November, with particularly sharp increases in less vaccinated, more rural counties. In Maryland, Caroline, Garrett and Allegany counties have seen the most significant changes in community transmission. Statewide, covid-related hospitalizations hit 963 on Friday, compared to under 700 in early November.

Officials of Maryland’s biggest counties said Friday afternoon that news of the three omicron cases was no reason to panic, but urged residents to be take greater precautions while thinking about the coming holiday season.

“We have been anticipating and preparing for this,” Montgomery County assistant chief administrative officer Earl Stoddard said in a tweet. “No reason to panic. Get boosted if you are eligible.”

In Howard County, where 76 percent of residents are fully vaccinated, officials said they were monitoring details of the three cases closely but thought it was too early to decide whether to reinstate sweeping precautions, such as a countywide indoor mask mandate.

But Boris Lushniak, dean of the University of Maryland School of Public Health, said local officials should act as prudently as possible while uncertainties over the omicron variant play out. Because not every positive coronavirus case in the region is genetically sequenced, it’s likely that there are more than just three cases of the omicron variant that have gone undetected, he said. “Right now, there’s enough uncertainty that we should really reconsider mask mandates,” Lushniak said.

These precautions, while unpleasant, can help buy the region time against the virus as officials step up surveillance through more testing and genetic sequencing.

Earlier this week, Hogan stressed the need for residents with symptoms and those traveling to get tested. He said the state was distributing rapid tests, making them available at local health departments, libraries and other community centers. He also said that the test would be available at the international terminal at Baltimore-Washington International Marshall Airport, where nearly 7,000 international passengers arrive weekly.

In Virginia, the state health department is increasing its testing program to identify strains. The state’s central laboratory has the capacity to do whole genome sequencing — the process that can identify variants — for 250 to 300 cases per week, according to Health Department spokesperson Logan Anderson.

In addition, the state has agreements with the University of Virginia, Virginia Tech and several private laboratories to perform sequencing, Anderson said. Positive coronavirus tests are being referred to the labs for sequencing if they meet criteria that could make them likely to contain a variant, such as if the person being tested had been exposed to someone with a known variant, was reinfected with the virus or had been traveling. State officials said they are actively contacting labs and hospitals around the state to try to identify cases that merit further testing. “It is an increasing number of positive samples that are being tested,” Anderson said via email.

Hogan said that the cases in Maryland were confirmed by the state Health Department in coordination with its partners. Earlier this year, the state entered into agreements with Johns Hopkins and the University of Maryland to more than double the state’s real-time variant surveillance, he said.

“If it’s not already here, it will be here shortly,” Patrick Ashley, the D.C. health department’s head of emergency response, said of the strain Friday during a D.C. Council meeting.

Council member Elissa Silverman (I-At Large) asked why the Health Department issued an “advisory” on Thursday asking all residents to wear masks indoors, rather than reinstating the legal mask requirement that Bowser just rescinded two weeks earlier despite the objection of the majority of the council. “Why not just do that, given omicron and concerns about transmission, community spread?” she asked.

“We’re not quite there,” Ashley said, noting that health experts don’t yet know whether omicron is significantly more perilous than other variants.

Silverman asked what numerical metrics would signal that the city needs a mask requirement again, and Ashley said he could not answer.

Gregory S. Schneider and Julie Zauzmer Weil contributed to this report.