About two dozen sailors on a U.S. Navy warship — or roughly 25% of the crew — have now tested positive for COVID-19, keeping the ship sidelined in port at Naval Station Guantanamo Bay in Cuba Monday, according to U.S. defense officials.

The USS Milwaukee has a crew of a bit more than 100, and it was forced to pause its deployment late last week because of the coronavirus outbreak. The defense officials, who spoke on condition of anonymity to discuss details of the outbreak, said the number of infected sailors is staying relatively constant at this point.

The USS Milwaukee, a smaller, stealthier combat ship, is the first Navy ship this year to have to interrupt its deployment at sea.

It began its deployment from Naval Station Mayport in Jacksonville, Florida, on Dec. 14, and had stopped for a scheduled port visit. The ship was heading into the U.S. Southern Command region.

Another warship, meanwhile, had to postpone its movement out to sea earlier this month due to a separate outbreak. Navy Cmdr. Sean Robertson, spokesman for 3rd Fleet, said the USS Halsey, a destroyer, delayed its homeport move from Pearl Harbor, in Hawaii, to San Diego because a significant number of the crew became infected with COVID-19. The ship was finally able to leave Hawaii on Sunday. The move is not a deployment, but a transfer to a new home station for the crew.

A Navy official said roughly one-third of the Halsey crew tested positive for the virus, and most had only mild symptoms or none at all. A destroyer has about 300 crew members. The official spoke on condition of anonymity to provide details on the crew impact.

Robertson said the crew was nearly 100% vaccinated and no one was taken to the hospital. Vaccine booster shots were made available for the crew. Robertson also said some of the samples have been tested and all were the omicron variant.

The Navy said in a statement Friday that the USS Milwaukee’s crew was “100% immunized” and that all of those who tested positive for COVID-19 were being isolated on the ship away from other crew members.

The U.S. officials said Monday that the Navy believes the total vaccination of the crew is the key factor in controlling the outbreak.

According to the Navy’s statement, “a portion” of those infected are having mild symptoms, and the specific variant is not yet known. COVID-19 cases have surged across the country as a result of the highly contagious omicron variant.

Other Navy ships were sidelined during the early months of the virus outbreak last year.

The first major military outbreak of the virus happened early last year on a Navy warship, the USS Theodore Roosevelt, an aircraft carrier that was operating in the Pacific. The Roosevelt was sidelined in Guam for nearly two months, and more than 1,000 of the 4,800 crew members tested positive. One sailor died, and the entire crew went through weeks of quarantine in a rotation that kept enough sailors on the ship to keep it safe and running.

According to the latest data released by the Navy, more than 98% of all active-duty sailors have been fully vaccinated.

(AP)