As the highly contagious delta variant surges across the world, the health and safety protocols established for cruise ships are being put to the test. Over two weeks in late July and early August, 27 coronavirus infections were identified aboard the Carnival Vista cruise ship sailing out of Galveston, Texas.

One of those infected, a passenger, later died.

It was the highest number of cases aboard a ship reported since June, when cruises restarted in the Caribbean and United States, and the first death.

The passenger and 26 crew members were immediately isolated after testing positive for the virus. Contact tracing and further testing was conducted, with no new cases reported by Aug. 11, when the ship arrived at the port of Belize City on the northeastern coast of Central America, Carnival said.

Though the ship sailed out of Texas, which bans businesses from requiring vaccinations, more than 96% of passengers were vaccinated and all but one crew member was fully vaccinated, according to the Belize tourism board.

Most infected crew members were either asymptomatic or experienced mild symptoms of the virus, but Marilyn Tackett, a 77-year-old passenger from Oklahoma, was admitted to the hospital in Belize and put on a ventilator after experiencing respiratory complications. Days later, she was evacuated to a hospital in Tulsa, Oklahoma, where she received treatment, but on Aug. 14 her condition worsened, and she died, according to a statement issued by her family on a crowdfunding page set up to help pay for her care.

Tackett’s family declined to comment on the incident.

“We are very sorry to hear about the death of a guest who sailed on Carnival Vista,” Carnival Cruise Line said in a statement. The cruise line said that it was highly unlikely Tackett contracted the coronavirus aboard the ship, which left Galveston on July 31, and that she had received expert medical care onboard before being evacuated.

The cruise line did not test vaccinated passengers before they embarked for the cruise.

Last week, the Centers for Disease Control and Prevention issued a new advisory, warning people with increased risk for severe illness from COVID-19 to avoid travel on cruise ships, irrespective of their vaccination status.

Carnival is not the only cruise line to have seen an uptick in cases. Earlier this month, Royal Caribbean had six guests test positive onboard its Adventure of the Seas ship.

The companies have responded to the recent increase in cases by introducing pre-departure testing requirements for all passengers. Carnival also added a mask mandate on Aug. 7 for all vaccinated and unvaccinated guests in indoor areas and banned smoking in the casino.

“The protocols are designed to flex up and adapt,” said Chris Chiames, the chief communications officer for Carnival Cruise Line, in a telephone interview. “That’s what they’ve done here in the context of their desire to mitigate and minimize the threat of COVID, which is everywhere, unfortunately, and it’s going to remain everywhere for a long time.”

“We never suggested our ships would be COVID free,” he continued. “But we designed our protocols to meet and exceed the guidelines of the CDC and we will continue to be vigilant while continuing to focus on giving our guests a great vacation.”

Michael Bayley, CEO of Royal Caribbean, said the cruise line was typically seeing one or two positive cases out of more than 1,000 guests a week per ship. More than 90% of passengers are vaccinated, he said, and because of preboarding testing requirements two to 10 guests are prevented from boarding ships each week because they test positive.

But, Bayley said in a candid Facebook post addressing the current coronavirus situation, “Testing captures status at a point of time and if the guest is incubating infection, then the test will miss it.” The vaccinated guests who test positive typically are asymptomatic, he said in the post.

Some cruise lines say passengers have canceled amid concerns about the risks of the delta variant, but many sailings are fully booked through the rest of year because of pent-up demand.

Many cruise enthusiasts with upcoming trips believe that cruise ships are one of the safest ways to travel during the pandemic because of the high percentage of vaccinated passengers and crew, added testing requirements and stringent health and safety measures enforced on board.

“It’s very comforting boarding a cruise ship knowing that most people are vaccinated and everyone is tested,” said Aidan Alexander, 62, an avid cruiser from Florida who has eight sailings booked through 2022. “When you get on a plane or stay in a hotel you don’t know anyone’s vaccination or COVID status and that makes it very difficult to relax and unwind.”

John Ioannidis, an epidemiology professor at Stanford University, disputes that notion. In an airport, on a plane or in a hotel, he said, “you only get exposed for a few hours, whereas on a cruise ship you could get exposed for many days and weeks. It’s a kind of cumulative exposure.”

But he said the health and safety protocols implemented by cruise companies will likely avert the major disasters and deaths that were seen in the initial stages of the pandemic last year.

“I think that it’s fair to say that it’s likely that the outbreaks will not be left to grow to the same extent as they did in the outbreaks in the first wave of the pandemic,” he said.

Christina Perez, 56, a passenger who was on board the Carnival Vista when the virus cases were identified earlier this month, said the cruise line dealt with the situation well and she felt safe throughout her trip.

“It was still an amazing vacation. The crew took great care of us and kept us informed and managed to contain the situation very quickly,” Perez said in a telephone interview.

“I think it’s getting risker to travel now with the new variants, even on cruises, but at least if there is an outbreak on a cruise ship there is a plan and you know you’ll be taken care of,” she said.

© 2021 The New York Times Company