Cruise lines say it's safe to set sail. Health experts aren't convinced.

Travel and cruise industry advocates are clamoring for ships to be allowed to sail again from U.S. ports. They're calling on the Centers for Disease Control and Prevention to lift coronavirus restrictions by July, saying it would be in keeping with President Joe Biden's goal of getting the country "closer to normal" by Independence Day.

Major cruise lines halted excursions from the U.S. in March of last year, when the CDC issued a "no-sail" edict that continues to bar passenger cruise ships from leaving domestic ports. 

The health agency's stance "does not reflect the industry's proven advancements and success operating in other parts of the world, nor the advent of vaccines, and unfairly treats cruises differently," Kelly Craighead, CEO of Cruise Lines International Association (CLIA), said this week in a statement. "Cruise lines should be treated the same as other travel, tourism, hospitality and entertainment sectors."

During the past eight months, cruise ships have resumed sailing in Europe, Asia and the South Pacific, with nearly 400,000 passengers participating in what the Cruise Lines International Association (CLIA) calls "a highly-controlled resumption of cruising." The trade group found less than 50 reported cases of the coronavirus in the public reports it tracks. Additional sailings are planned in the Mediterranean and Caribbean later this spring and summer, Craighead noted.

Florida Governor Ron DeSantis on Friday also blasted the federal government's continued pandemic ban on cruise ships using U.S. ports, threatening legal action if one of the Sunshine State's biggest tourism sectors is not allowed to restart soon.

"Is it OK for the government to just idle an industry for a year?" the Republican governor said at a news conference at Port Canaveral with leaders from Carnival, Norwegian, Disney and Royal Caribbean cruise lines. DeSantis said people can decide for themselves what they are willing to risk.

Florida is home to three of the world's busiest ports: Miami, Port Canaveral near Kennedy Space Center, and Port Everglades near Fort Lauderdale. Millions of travelers typically cruise from Florida each year, and the industry generates billions for the state's economy.

DeSantis said the continued ban is only hurting Florida, with no effect on the pandemic as cruises resume elsewhere around the world and Americans head to the nearby Bahamas to board ships.

CLIA's call drew support from Zane Kerby, president and CEO of the American Society of Travel Advisors, who said it is "unconscionable for the CDC to single out cruising as the one activity that poses such unique risks."

"Sources of super-spreading outbreaks"

But health experts aren't convinced cruises can resume safely , noting that having thousands of people aboard a vessel at one time has long carried the risk of widespread infection. The industry is jumping the gun, they suggest, noting the still high number of COVID-19 cases in the U.S. and a death toll exceeding 547,000.

"Cruises are very often sources of super-spreading outbreaks, and not just for COVID," Tara Kirk Sell, a senior scholar at the Johns Hopkins Center for Health Security, told CBS MoneyWatch. "You have confined space and close quarters that just lend themselves to the spread of disease." 

Dr. Paul Sax, clinical director of the infectious diseases division at Brigham and Women's Hospital in Boston, agreed. 

"From the infectious diseases perspective, cruises represent high-risk activities for contagion given the fact that so many people are confined to a relatively small space," he said. "This was true even before COVID-19."

Cruise ships are often settings for disease outbreaks because of their closed environment and contact between travelers from many countries, according to the CDC. Cruise lines have long contended with outbreaks of the norovirus, for instance, one of which sickened more than 300 passengers and crew on a Princess Cruises ship in February of 2020.

Both Sell and Sax believe the push to reopen U.S. ports is premature, citing the ongoing pandemic. 

"I know there are people out there who love cruising, but the industry shouldn't be leading the charge back to normal," Sell said.

Sax added in an email: "Before these go forward again, it would be optimal to have case numbers in the USA drop to lower levels. Companies should also consider requiring COVID-19 immunizations for both staff and passengers."

CLIA called vaccinations a "game-changer" but stated that the group did not have a vaccine policy. "The organization and its members are exploring a workable approach for how to consider vaccinations, once widely available, as part of robust protocols," the trade association stated.

A spokesperson for the CDC said the agency's conditional sailing order remains in effect until November 1, 2021. "Returning to passenger cruising is a phased approach to mitigate the risk of spreading COVID-19," the spokesperson said in an email to CBS MoneyWatch. Details for the next phase are currently under review, the spokesperson added.

Cruisers heading to overseas ports

Americans intent on taking a cruise are finding workarounds, with multiple cruise lines setting off from the Bahamas, Bermuda and a number Caribbean islands, allowing them to sail without entering a U.S. port.

Royal Caribbean is among those cruise operators planning to mandate vaccinations for adult passengers and crew. People under 18 years of age will have to provide proof that they have tested negative for the coronavirus. Luxury line Crystal is also only letting those who have been vaccinated on its ships.

The CDC does not have jurisdiction over ships that operate outside of U.S. waters without intending to return to U.S. waters. The agency still recommends that all people avoid travel on cruise ships worldwide "because the chance of getting COVID-19 on cruise ships is high, since the virus appears to spread more easily between people in close quarters aboard ships."

The Associated Press contributed to this report.