With just days to go before the CDC’s “No Sail” order is set to expire, the agency has issued a warning advising U.S. travelers to defer all cruise travel.

“CDC typically posts travel health notices for countries and other international destinations, not transportation, such as ships, airplanes, or trains. Because of the unprecedented nature of the novel coronavirus pandemic, and the increased risk of transmission of COVID-19 on cruise ships, the U.S. government is advising U.S. travelers to defer all cruise travel,” the CDC said, in a Level 3 alert posted to its website.

The CDC said reports of COVID-19 on cruises highlight the risk of infections to cruise passengers and crew, although it did not elaborate on these reports.

“Like many other viruses, COVID-19 appears to spread more easily between people in close quarters aboard ships and boats. As the COVID-19 pandemic continues, there remains a risk of infected passengers and crew on board cruise ships,” the agency said.