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.

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

The omicron variant has sent case levels soaring 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.