TAMPA, Fla. (WFLA) — A fully immunized U.S. Navy warship was held at port after a number of its vaccinated crew tested positive for COVID-19.

The USS Milwaukee, a littoral combat ship, was held at Naval Station Guantanamo Bay after its crew of “100% immunized” sailors experienced a small outbreak of infections, according to an announcement from the U.S. Navy.

Sailors who tested positive were isolated onboard and away from other crew members, the announcement states. Only a portion of those infected exhibited mild symptoms. The Navy did not clarify the number of infected sailors, only that “The vaccine continues to demonstrate effectiveness against serious illness.”

While the specific COVID variant has yet to be determined, officials said all the Centers for Disease Control and Prevention (CDC) guidelines have been followed, including contact tracing and testing protocols.

Earlier in the year, the military set a deadline for nearly 350,000 Navy sailors and more than 179,000 Marines to be fully vaccinated by Nov. 28, 2021.

The USS Milwaukee departed from Mayport, Fla. on Dec. 14 for its regularly scheduled deployment to the U.S. 4th Fleet area of operations.