The announcement sounded like every landlocked cruise fan’s dream: Tiny operator SeaDream Yacht Company was promising a safe, luxurious voyage from Barbados, a “much-needed escape” during a brutal year.

“The goal is to create a COVID-19 negative bubble, where guests can relax and enjoy the safety of the ship,” a news release said.

SeaDream’s bubble burst quickly; seven passengers and two crew tested positive despite multiple tests required before boarding the small ship, where they were not initially required to wear masks. The company canceled cruises for the rest of the year and issued a dejected update: “The company will now spend time to evaluate and see if it is possible to operate and have a high degree of certainty of not getting Covid.”

That’s the question the rest of the industry has been asking for the better part of a year, even before global cruising shut down in March. While voyages have restarted in other parts of the world with some success, no mainstream cruises have left from the United States — and probably won’t for many more months as operators and health authorities continue to hammer out plans for what coronavirus-era cruising will look like.

One thing has become clear: Pre-cruise testing does not guarantee a safe bubble.

YouTube content creators Ben Hewitt and David McDonald, who run Cruise With Ben & David, were on the SeaDream cruise as it took its first Caribbean voyage. Hewitt said they felt comfortable taking their first cruise in eight months with two tests required before boarding and constant cleaning and outdoor activities on the ship, though they were surprised that masks were not required.

“I think it really does highlight the issue about whether or not tests are an effective method of stopping covid, especially from getting on aircraft, cruises, whatever,” said Hewitt, 35. “It’s something that can seep through no matter what test you have.”

Tara Smith, a professor of epidemiology at Kent State University who has written about cruising, said people could be exposed and incubating the virus but still have an undetectable viral load when they get tested, or they could be exposed after testing and then become infectious after they board.

“Either way, tests are helpful but they are not foolproof,” she said in an email.

And they aren’t always consistent. After Royal Caribbean launched “cruises to nowhere” in Singapore at the beginning of the month, one of its early voyages ended early and another was canceled after a passenger fell ill and tested positive for the virus on board. He had negative test results before setting sail, and follow-up tests conducted by the health ministry confirmed he did not have the coronavirus after all.

Rather than depending solely on tests as a precaution, cruise lines have crafted plans in consultation with health experts meant to keep coronavirus off — but also deal with the virus if it sneaks on.

A panel of experts who consulted for Royal Caribbean Group and Norwegian Cruise Line Holdings recommended every guest be tested 24 hours to five days before a cruise. “If logistically and financially feasible,” the group recommended a second test immediately before boarding — similar to the protocol SeaDream used.

The world’s largest cruise operators have pledged to require distancing on ships, private islands and during shore excursions; mandate masks whenever passengers and crew cannot be physically distanced; increase the amount of fresh air that circulates; make contingency plans in case passengers end up sick and need to be isolated or transported; and crack down on shore excursions.

Group dinners with strangers who become friends over the course of a voyage — a staple of traditional cruises in normal times — are probably to be a thing of the past once cruising starts again, at least until the virus is under control.

“Unfortunately, no setting is immune from the virus; however, our members are fully committed to implementing multiple layers of enhanced prevention and response measures to mitigate risk and protect public health,” Bari Golin-Blaugrund, a spokeswoman for Cruise Lines International Association, said in an email. She said the industry has learned from more than 200 cruises that have taken place since the beginning of July.

“When enhanced protocols are in place and rigorously followed, they are working as intended, which is to mitigate the risks associated with the introduction and transmission of the virus onboard,” she said.

Still, Smith warned, the virus can slip through layers of protection. She believes people should stay off cruise ships for now, as does the Centers for Disease Control and Prevention, which recommended all people avoid cruises because of the high risk of contracting the coronavirus.

“I do think it’s quite probably that infected people will end up on cruises, and even with those interventions in place, an outbreak could occur before people are identified as positive,” she said, noting that masks can’t be worn while eating and drinking. “These cruises are not a sanctuary away from the virus, as much as people may like to think so.”

Even as cruise lines learn from sailings elsewhere in the world, they are preparing for a long wait in the United States. A restart is still months away; major operators have canceled cruises through the end of February and March, but it will probably be even longer given the steps they have to take to meet CDC requirements to sail again. Some of the specific instructions that will be required by the agency have not even been provided yet.

That delay will put a resumption of cruising closer to the distribution of a vaccine — a development observers expect will be a boost for the industry.

“If everyone’s vaccinated, or if a large portion is vaccinated by next summer, the cruise industry should pick up relatively well,” says Andrew Coggins, a professor at Pace University who teaches cruise industry management.

Roger Frizzell, chief communications officer for Carnival Corp., called the vaccine “certainly a positive development for cruising and the broader travel and hospitality industries.”

He added: “But we also have implemented enhanced safety and health protocols on our ships in close coordination with our medical and science experts along with health and government authorities.”

Smith warned that cruise passengers should not expect even a vaccine to eliminate all risk.

“Widespread vaccination would not completely prevent the potential for infection, but coupled with other interventions like testing and masking, it would significantly reduce risk of serious infection,” she said.

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