MIAMI — 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.