Two of the world’s largest cruise operators insist their ships are no more vulnerable to the spread of the new coronavirus than other public places.

The cruise industry has long pushed back at the idea that the close quarters on ships may be ripe conditions for the spread of disease. And major players continue to maintain that position, even though there have been more than 3,000 COVID-19 cases and dozens of deaths associated with ships, according to the Cruise Lines International Association. Top executives at Norwegian Cruise Line Holdings Ltd. and Royal Caribbean Cruises Ltd. were asked last week to acknowledge that people are more likely to get coronavirus on a cruise ship than in the general public.

“No, I don’t believe” that, Frank Del Rio, the CEO of Norwegian, said in a Zoom interview, where he was joined by Richard Fain, head of Royal Caribbean. “I think done correctly a cruise ship — because it is a controlled environment — can be among the safest places on Earth.”

The CEOs said they have formed a new partnership on health protocols to implement when they start sailing again. The group, the Healthy Sail Panel, is being led by former U.S. Food and Drug Administration Commissioner Scott Gottlieb and former U.S. Health Secretary Mike Leavitt.

The industry has wrestled for years with the issue of shipboard illnesses, including outbreaks of the norovirus vomiting bug. The cruise association, the lobbying arm for the industry, citing data from the Centers for Disease Control and Prevention, says guests are far more likely to get norovirus on land than on a ship. But the CDC cites cruise ships, along with schools, health care facilities and restaurants, as one of the “common settings of norovirus outbreaks.”

On March 8, the U.S. State Department said Americans, especially those with underlying conditions, should avoid cruise travel due to “increased risk of infection.” In a memo updated June 3, the CDC said there’s a “high risk” of COVID-19 spread on cruise ships because people spend time close together, interact with travelers from around the world, and are served by crew members who may bring infections aboard from other ships.

Separately, a study in the CDC’s Morbidity and Mortality Weekly Report in March found that traces of the coronavirus lingered in cruise-ship cabins for as many as 17 days after passengers left.