A Navy combat ship deployed to intercept drug trafficking in the Caribbean and East Pacific is stuck in the port at Guantánamo Bay, Cuba, with a coronavirus outbreak among its fully vaccinated crew.

Only some of those infected onboard the ship, the U.S.S. Milwaukee, were experiencing mild symptoms, said Commander Kate Meadows, a Navy spokeswoman. It was not clear how many infections involved the Omicron variant, which continues to gain dominance rapidly around the world.

The crew held an open-air Christmas service on the pier on Saturday, which allowed the sailors to remain socially distanced and to follow public health guidelines, according to Commander Meadows.

“They are using the open space and fresh air for as many safe activities as they can,” she said. “The chefs onboard are making a special Christmas meal today for everyone.”

The Milwaukee had more than 100 sailors plus a helicopter combat crew and Coast Guard law enforcement unit on board when it left its home port in Jacksonville, Fla., on Dec. 14 as part of the U.S. Southern Command’s efforts to fight drug trafficking. The ship made a refueling and resupply stop at Guantánamo Bay on Monday and extended its stay there because of the outbreak.

Commander Meadows added that the sailors had been confined to the pier and had not entered the base since arriving, sparing the small community at Guantánamo Bay the possibility of being exposed.

In a statement on Friday, the Navy said that “the ship is following an aggressive mitigation strategy” and that “the vaccine continues to demonstrate effectiveness against serious illness” among the crew.

Before the Milwaukee left Florida, Brian A. Forster, the ship’s commanding officer, said in a Navy news release that many of the crew members were on their first deployment and “eager to see the world and accomplish missions.”

In March 2020, one of the military’s first encounters with the virus occurred aboard the aircraft carrier Theodore Roosevelt. The ship docked in Guam, in the South Pacific, and ended up stranded there for months after dozens of sailors were infected and one died. The ship’s commander at the time sent a letter to Navy officials pleading for help tackling the outbreak and criticizing the Navy’s failure to provide the proper resources. He was removed from command of the ship after the episode.

Active-duty troops in the Army and Navy were fired this month over their refusal to get vaccinated after President Biden mandated vaccination for the armed services in August. But there were only a small group of holdouts last week, with the Navy reporting that more than 98 percent of its members had been vaccinated.