(CNN) — After a "small number of positive cases" of Covid-19 were detected aboard a Carnival Cruise Line ship, a new fleetwide mask policy requiring all guests to wear masks in some indoor areas was implemented ahead of schedule, the cruise line said.
Carnival did not immediately say exactly how many positive cases had been detected aboard Carnival Vista, which departed out of Galveston, Texas.
The Covid-positive individuals are in isolation and their close contacts have been identified and tested, Carnival said in a statement.
"Our pre-established protocols of vaccinated guests and crew, testing, enhanced medical capabilities and contact tracing anticipated the potential for positive cases, and they are designed to adapt to various scenarios," the statement said.
The new policy that requires all guests, even the vaccinated, to wear masks in certain indoor areas was set to go into effect for cruises departing on or after August 7, but the positive cases prompted an immediate start aboard Carnival Vista Wednesday evening.
The voyage will go on as planned, Carnival said.
The cruise line will continue to operate vaccinated cruises as defined by the US Centers for Disease Control and Prevention. The CDC requires 95% of both passengers and crew to be vaccinated. Carnival said its crew is fully vaccinated.
In addition to its new mask rule, Carnival is also adding a pre-cruise testing requirement for all vaccinated guests. Fully vaccinated guests must have a negative Covid-19 test result (PCR or antigen) taken within three days of departure.
That rule goes into effect on August 14. Both new requirements are slated to be in place through October 31.