In a statement, Royal Caribbean said that each person who had tested positive on arrival immediately went into quarantine, while six people who had tested positive onboard had already disembarked the ship mid-voyage.
Those who tested positive were either asymptomatic or had mild symptoms, said the statement.
The Symphony of the Seas had departed on 11 December with 6,091 passengers aboard, 95 per cent of whom were fully vaccinated.
It is the world’s largest passenger cruise ship, with capacity for 9,000 guests and crew.
The ship had left Miami before visiting St. Maarten, St. Thomas in the U.S. Virgin Islands, and CocoCay, the operator’s private island in the Bahamas.
Royal Caribbean says it imposes stringent health rules on all its passengers.
All holidaymakers aged 12 and above must be fully vaccinated to board its ships, and must test negative before departure.
The cruise line also says it “strongly recommends” guests receive a booster dose prior to their trip, but this is not enforced.
However, passengers James Johnson and Connor O’Dell told the Miami Herald that they weren’t convinced by Royal Caribbean’s health and safety policies onboard the Symphony cruise, after two members of their party tested positive.
They told the Florida news outlet that staff onboard had given conflicting information about whether their relatives should quarantine onboard, and could not provide their group with Covid tests.
“I bought into the safety aspect,” said O’Dell.
“I was reading the literature they have online and thought, ‘How much safer can you get?’ Everyone’s vaccinated and has to get tested. And then you get on board and find yourself in the middle of the outbreak.”
Cruises have been permitted since July, with many leaving from different locations this summer and autumn.
The cruise industry worldwide has been decimated by the Covid crisis, following several high-profile outbreaks at the beginning of 2020.
However, many fear the vessels are still high risk for outbreaks of the virus.
In August, 27 people - 26 of them crew - tested positive for Covid aboard a Carnival cruise ship docked in Belize.
Meanwhile, two passengers aboard the Celebrity Millennium tested positive partway through a cruise in June.
The Symphony of the Sea’s plans won’t be affected by this latest outbreak, according to the Miami Herald.
It reports that the vessel has already left Miami for a new trip to Cozumel, Mexico, and is expected to arrive by 11am local time on 20 December.
A spokesperson for Royal Caribbean says: “[The 48 passengers] were identified as a result of immediate contact tracing after a guest tested positive. The cruise sailed with 95% of the onboard community fully vaccinated, and 98% of those who tested positive were fully vaccinated.
“Each person quickly went into quarantine. Everyone who tested positive was asymptomatic or mildly symptomatic, and we continuously monitored their health.”
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