RELATED: Virus Experts Have Stopped Going to These 4 Places as Delta Surges. In June, cruises began departing from the U.S. once more, over a year since they had been suspended due to the pandemic. But just as cruise ships had been a hotspot for virus outbreaks in 2020, they’re proving to still be hotbeds of transmission, even in the post-vaccine era. Over the course of two weeks in late July and early August, 27 COVID cases were identified aboard a Carnival Vista cruise ship sailing out of Galveston, Texas, despite more than 96 percent of passengers being vaccinated, The New York Times reported. One of the infected passengers, a 77-year-old woman named Marilyn Tackett, died even though she was reportedly fully vaccinated before embarking on the cruise. And this isn’t the only cruise line to experience recent outbreaks. In late July, a Royal Caribbean cruise had six guests test positive onboard its Adventure of the Seas ship. The infections occurred despite the ship requiring all crew and passengers 16 and older be fully vaccinated against the virus at the time, per The Washington Post. Luis Ostrosky, MD, the division chief for infectious diseases at University of Texas Health, told CNBC that while all travel is risky amid the Delta variant, cruises come with extra risks that cannot be ignored, such as shared common areas, buffet restaurants, shows in theaters, and the inability to leave the boat if an outbreak does occur at sea. “It’s just a recipe for transmission,” Ostrosky said. Even outside of the pandemic, cruises have often fallen victim to outbreaks of other contagious respiratory or gastrointestinal viruses. In 2019, a Royal Caribbean cruise had to cut its journey short after 475 passengers and crew members got infected with a norovirus.ae0fcc31ae342fd3a1346ebb1f342fcb RELATED: For more up-to-date information, sign up for our daily newsletter. Many cruise enthusiasts maintain that cruise ships are one of the safest ways to travel right now during the ongoing pandemic because of the high percentage of vaccinated passengers and crew. Aidan Alexander, a frequent cruise traveler who has eight cruises booked through 2022, told the NYT that it is “very comforting” boarding cruises knowing most people are vaccinated, while “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.” Virus experts disagree. John Ioannidis, MD, an epidemiology professor at Stanford University, told the NYT that in an airport, on a plane, or in a hotel, “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.” And although several cruise companies are requiring vaccinations for all passengers, experts say that just isn’t enough while Delta surges. “We can try to do cruises as safely as possible, but we are going to have breakthrough cases,” Ostrosky told CNBC. According to Ostrosky, while vaccination still significantly reduces your chances of hospitalization or death from COVID, the Delta variant’s increased transmissibility means that vaccination “no longer guarantees that you’re not going to acquire the infection, or be able to transmit it.” RELATED: If You See This Inside Any Business Right Now, Leave Immediately, Experts Say.