CDC says all travelers, fully vaccinated or not, should avoid going on cruise ships

• The CDC has raised its cruise travel warning to the highest level.
• Cruise ships have seen a spike in COVID-19 cases amid spread of the Omicron variant.

The US Centers for Disease Control and Prevention raised its cruise travel warning to the highest level on Thursday as COVID-19 cases continue to spike aboard cruise ships amid the spread of the Omicron variant.

The CDC recommends all travelers — vaccinated or not — avoid cruising, saying the probability of getting COVID-19 on a cruise ship is "very high," even if the passenger is fully vaccinated with a booster shot.

"It is not possible for cruising to be a zero-risk activity," a spokesperson told Insider on Monday, noting that COVID-19 can spread "easily" on a cruise ship due to its tight quarters.

Travelers who still want to cruise should be tested for COVID-19 one to three days before sailing and again three to five days after the trip, the agency recommended. Unvaccinated passengers should also quarantine for five days after cruising.

The Cruise Lines International Association told Insider in a statement that it is "disappointed and disagrees" with the elevated travel warning, calling the agency's decision "particularly perplexing."

"Cases identified on cruise ships consistently make up a very slim minority of the total population onboard," the trade association said, adding that most of the cases have been asymptomatic or "mild."

This update comes as the CDC is investigating over 90 cruise ships in the wake of increased COVID-19 outbreaks aboard the vessels. In the last two weeks of December, cruise ships have reported over 5,000 coronavirus cases, 31 times the cases reported in the first two weeks of the month, the CDC told Insider in a statement.