The coronavirus has spread to at least a dozen US Navy sailors assigned to ships in San Diego, California, according to Navy statements.

The first three coronavirus infections aboard San Diego-based US Navy warships emerged among sailors assigned to the amphibious assault ship USS Boxer and Littoral Combat Ship USS Coronado. The Navy has changed its policy and is no longer reporting which ships infected sailors serve aboard.

Since the policy change, the Navy has reported nine additional cases among sailors assigned to ships based in San Diego.

As of Sunday, at least 111 US service members have reportedly tested positive for the virus.

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The novel coronavirus has spread to at least a dozen US Navy sailors assigned to ships in San Diego, California, according to Navy statements.

The first sailor aboard a US warship to test positive for the coronavirus was a service member aboard the amphibious assault ship USS Boxer, currently at port in San Diego. That first sailor tested positive on March 13. A few days later, the Navy announced that a second sailor aboard the ship had the virus.

As the virus spread aboard the Boxer, the Navy revealed that a sailor aboard the Littoral Combat Ship USS Coronado, also in San Diego, had tested positive.

Two sailors assigned to San Diego-based ships tested positive on Thursday, two more were confirmed to have the virus on Friday, and five tested positive on Saturday, the Navy announced in a series of statements this week.

All sailors who have tested positive have been isolated off ship, as have individuals they had close contact with recently.

The Navy initially announced which ships the sailors served on, but it has since changed its policy, which is now “to only release the number of positive cases and the geographic location of those sailors,” US Pacific Fleet told The San Diego Union-Tribune.

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Aboard affected ships, the Navy has launched an “aggressive mitigation strategy” to limit the spread of the virus. The approach involves screening all personnel coming aboard the ships, enforcing social distancing, and cleaning and bleaching the ships twice daily, among other things.

Navy ships can be difficult to protect from outbreaks though.

Last year, for example, the Whidbey Island-class dock landing ship USS Fort McHenry experienced a mumps outbreak. The vaccine-preventable illness hit the ship hard, infecting 28 people despite efforts to quarantine the infected and disinfect the ship. There is currently no vaccine for the coronavirus.

As of Sunday, the number of infected US military service members had climbed to 111, significantly higher than the 67 reported Friday, according to multiple reports.

The coronavirus that first appeared in China is now a pandemic that has infected more than 328,000 worldwide and claimed more than 14,000 lives. In the US, more than 25,000 people have tested positive, and over 300 people have died.