The Centers for Disease Control and Prevention is now urging everyone to avoid cruise ships, including those who have been vaccinated against COVID-19. 

The CDC on Thursday issued the recommendation to “avoid cruise travel, regardless of vaccination status.” The agency at the same time said it was upgrading its travel health notice to the highest level of level 4, citing “increases in cases onboard cruise ships since identification of the Omicron variant.” 

The move comes as the CDC is investigating or observing around 90 cruise ships with COVID-19 outbreaks. On its website, the CDC lists dozens of ships that have received yellow color status, meaning they have met the threshold for a CDC investigation. “There has been an increase in the number of cruise ships meeting the COVID-19 case threshold for CDC investigation,” the CDC said.

As it raised the health notice level, the CDC warned Thursday that 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 you are fully vaccinated and have received a COVID-19 vaccine booster dose.” Those who do choose to travel on cruise ships, the CDC said, should make sure they’re fully vaccinated and have received a booster dose if eligible, and they should wear a mask in shared spaces. 

The Cruise Lines International Association trade group pushed back on the CDC’s recommendation, per Bloomberg, calling it “perplexing” because the number of COVID-19 cases on cruise ships “make up a very slim minority of the total population onboard — far fewer than on land.”