The US Centres for Disease Control and Prevention (CDC) eased its warnings for cruises by a notch from the highest level that led to a sailing hiatus, and recommended only fully vaccinated people take trips when sailings resume from US ports in a few days.

The CDC also recommended that travelers get tested 1 to 3 days before their trips and 3 to 5 days after their trips, Reuters reports.

The health regulator's updates comes after two passengers on Royal Caribbean Group's Celebrity Millennium tested positive, and cases of infection among crew members aboard its Odyssey of the Seas, forcing delay of its first trip.