Royal Caribbean Reported a COVID-19 Outbreak on the World's Biggest Cruise Ship

Royal Caribbean announced that 48 people on board its Symphony of the Seas, the world's biggest cruise ship, have tested positive for COVID-19

The ship, which docked in Miami over the weekend, had more than 6,000 passengers and crew, according to NBC News. The cruise featured a seven-night itinerary that left Miami on December 11 and visited St. Maarten, St. Thomas, and Royal Caribbean's private CocoCay island in the Bahamas before returning to Miami on December 18.

As is required by Royal Caribbean, all guests had to show proof of a negative COVID-19 test, taken no more than two days before the ship sailed. It was during the trip that a guest tested positive for COVID-19. That positive test led the cruise line to conduct wider contact tracing, which uncovered the additional cases.

"Each person quickly went into quarantine," Royal Caribbean told Health in a statement. "Everyone who tested positive were asymptomatic or had mild symptoms, and we continuously monitored their health." The cruise line had six people who tested positive for COVID-19 disembark earlier in the cruise, while the other guests who tested positive left the ship on December 18 when the trip ended.

Of those who tested positive, 98% were fully vaccinated, according to CNN. In fact, 95% of people on the entire ship were fully vaccinated.

All crew members on Royal Caribbean cruises must be fully vaccinated and tested weekly, according to the company. Royal Caribbean also requires that all guests ages 12 and up be fully vaccinated before sailing. Children who are between the ages of five and 11 who have been vaccinated can show their proof of vaccination and follow protocols for vaccinated guests; those who aren't vaccinated have to undergo COVID-19 testing to prove they don't have COVID-19. The cruise line also "strongly recommends" that guests receive their booster shot before cruising, when eligible.

Cruises were home to some of the earliest outbreaks of COVID-19 at the start of the pandemic. In the US, they were under a "no sail" order from the Centers for Disease Control and Prevention (CDC) for months before being allowed to sail earlier this year under strict regulations.

The CDC currently recommends that people who are not fully vaccinated against COVID-19 avoid traveling on cruise ships and points out that the risk of contracting COVID-19 on a cruise is "high." Many—but not all—cruise lines require full vaccination as a requirement for sailing.

The Royal Caribbean's COVID-19 cases aren't the only recent COVID-19 outbreak tied to a cruise ship. In early December, at least 17 people on board a Norwegian Cruise Line ship tested positive for the virus, despite the company's requirement that everyone on the ship be fully vaccinated against COVID-19.

But as Health previously reported, experts say it's not shocking that breakthrough COVID cases would happen on a cruise—even if everyone was fully vaccinated. "Obviously, there are breakthrough infections. That is always a risk," Reynold Panettieri, MD, vice chancellor for translational medicine and science at Rutgers University in New Jersey, previously told Health.

Even with the testing protocols that the most recent Royal Caribbean cruise had in place, it's still not totally unexpected that cases would pop up. Testing before boarding is not a perfect science, Thomas Russo, MD, professor and chief of infectious disease at the University at Buffalo in New York, previously told Health. "There could be people on the boat who were infected and were asymptomatic but not infectious enough to be picked up on a test at boarding," he said. "You could test negative when you get on the boat and subsequently develop an infection."