Fifty-five people have tested positive for Covid-19 aboard a Royal Caribbean International cruise ship that set sail Saturday from the southeastern US state of Florida, the company said.

The infections on the "Odyssey of the Seas" involved passengers and crew members, even though 95 percent of the people on board were vaccinated against the coronavirus, Royal Caribbean said late Wednesday.

Out of an abundance of caution the ship did not dock at the Caribbean islands of Curacao and Aruba, the last scheduled stops on its eight-day voyage, so it will remain at sea until it returns to Fort Lauderdale, Florida, on December 26.

The Odyssey is carrying 3,587 passengers and 1,599 crew members, according to USA Today newspaper.

The shipping company said all 55 of those infected have been vaccinated against the coronavirus and are asymptomatic or have mild symptoms.

Their close contacts have been quarantined for 24 hours before undergoing a Covid test.

Cruise ships, like this Royal Caribbean vessel, face a mounting challenge with the rise of the highly infectious Omicron variant of the coronavirus
Cruise ships, like this Royal Caribbean vessel, face a mounting challenge with the rise of the highly infectious Omicron variant of the coronavirus AFP / Sebastien SALOM-GOMIS

This is the second outbreak on a Royal Caribbean cruise ship in less than a week.

Last Saturday, the "Symphony of the Seas" returned to the port of Miami with 48 Covid-19 patients on board after a seven-day voyage in the Caribbean.

Several passenger ships suffered coronavirus outbreaks in the early months of the pandemic in 2020, leading to the suspension of cruise activities for more than a year.

The industry resumed operations in June with strong security measures in place to guard against possible contagion.

Royal Caribbean requires, for example, that its passengers over the age of 12 and its employees be fully vaccinated.

But the highly contagious Omicron variant of the coronavirus poses a new challenge for the industry.