Days ahead of the expiration of its No Sail Order, the CDC has updated its travel notice for US holiday-makers, advising them to defer all cruise travel.

The Centers for Disease Control (CDC) said that it was going against precedent by singling out a single mode of transport, but said cruise ships were particularly vulnerable to the spread of COVID-19 and raised its alter level for the industry to 3.

The move by the CDC is a huge blow to the US cruise sector, which had hoped to resume cruises in the coming weeks.

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The move took the cruise industry by surprise, coming so close on the heels of a wave of optimism following constructive meetings and an ongoing dialogue between the US government and cruise industry leaders.

It had been expected that the CDC might be about to rescind the No Sail Order, after cruise lines submitted detailed plans for the safe resumption of cruises, based on the experience of several lines that have resumed limited cruises in Europe.

“The CDC typically posts travel health notices for countries and other international destinations, not transportation, such as ships, airplanes, or trains,” the government agency said in its notice.

“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,” it added.

This is the first time the CDC has singled out a particular mode of transport.

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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.

The move may still be a precursor to the cancellation of the No Sail Order, with the CDC possibly intending to advise against cruise travel while not explicitly prohibiting it, or it could be an indication that the CDC plans to extend the No Sail Order into 2021.

An extension of the order was previously advocated by Director Robert Redfield, during a White House meeting in which he was over-ruled by Vice President Mike Pence.

The Trump administration has consistently called for the cruise industry to be allowed to resume, while pandemic experts have warned against such a move, given the ongoing rampant spread of the virus in the United States.