MIAMI (AP) — The U.S. Centers for Disease Control and Prevention warned people on Thursday not to go on cruises, regardless of their vaccination status, because of onboard outbreaks fueled by the omicron variant.

The CDC said it has more than 90 cruise ships under investigation or observation as a result of COVID-19 cases. The agency did not disclose the number of infections.

“The virus that causes COVID-19 spreads easily between people in close quarters on board ships, and the chance of getting COVID-19 on cruise ships is very high,” even if people are fully vaccinated and have received a booster, the CDC said.

In March 2020, as the coronavirus took hold in the U.S., the CDC put a halt to all cruises for what turned out to be 15 months. Last June, it allowed ships to resume sailing under new strict new conditions.

In August, as the delta variant surged, the agency warned people who are at risk of severe illness despite being vaccinated not to go on cruises.

The CDC on Thursday also recommended that passengers get tested and quarantine for five days after docking, regardless of their vaccination status and even if they have no symptoms.

Omicron has sent cases skyrocketing to unprecedented levels across the U.S., including Florida, the hub of the nation’s cruise industry. The state set another record this week for new daily cases, with more than 58,000 recorded Wednesday.

U.S. cruise lines have not announced any plans to halt trips, though vessels have been denied entry at some foreign ports.

Before the CDC announcement, Royal Caribbean Group said in a statement that omicron is leading to passenger cancellations and changes to itineraries, but that the mutant version is causing “significantly less severe symptoms than earlier variants.”

The company said that since cruising restarted in U.S. waters last spring, 1.1 million guests had traveled with its cruise lines and 1,745 people had tested positive for COVID-19, or about 0.16%.

It said that 41 people required hospitalization, and that no passengers hit with omicron had been taken to the hospital.

“We don’t like to see even one case, but our experience is a fraction of the comparable statistics of virtually any other comparable location or industry. Few businesses are subject to such intense scrutiny, regulation and disclosure requirements by so many authorities,” said Richard Fain, CEO of Royal Caribbean.

Most cruise lines require adult passengers to show proof of vaccination against COVID-19. Ships are allowed to relax measures such as mask use if at least 95% of passengers and 95% of crew are fully vaccinated.

Janine Calfo, 55, of Salt Lake City, put off a four-day Carnival cruise from Long Beach, California, to Ensenada, Mexico, earlier this month when she got a breakthrough case of COVID-19 three days before departure. She rebooked the cruise for February and is still set on going.

“This is my own personal opinion, but it looks like the omicron is going to be a quick burn,” said Calfo, who is asthmatic and plans to get the booster in a couple of weeks. “My cruise is over 40 days away.”

She added, though: “I think I will plan on getting travel insurance this time.”

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