The Centers for Disease Control and Prevention is warning travelers that have an “increased risk for severe illness” to avoid cruise ships, regardless of their vaccination status.

The new warning comes from the agency as an update to a previous recommendation that cautioned the unvaccinated about traveling on cruise ships.

According to the CDC, “Severe illness means that a person with COVID-19 may need: hospitalization, intensive care, a ventilator to help them breathe or they may even die.”

The guidance from the CDC refers to older adults, people with medical conditions, and those who are pregnant.

“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 CDC said on its website.

The change in guidance arrives as cases of the virus continue to surge across the U.S. as a result of the highly contagious Delta variant, even among vaccinated people.

Several cruise lines have implemented vaccination requirements for boarding their ships, operating fully vaccinated cruises from the U.S. for passengers 12 and older. Royal Caribbean and Norwegian Cruise Line have begun sailing with a proof of vaccine requirement.

In June, cruise lines began sailing in U.S. waters for the first time since suspending operating back in March 2020 at the height of the COVID crisis. Cruise ships were considered “superspreaders” of the coronavirus at the peak of the pandemic, with thousands of people contracting the virus on ships across the world.

The CDC issued a no-sail order that shut down the U.S. cruise industry, only lifting the order with a series of COVID safety measures that were required to be followed to begin sailings from U.S. ports.

Despite the safety measures, some cruise ships have reported a small number of COVID cases onboard their ships, with passengers and crew becoming infected by the virus during sailings.

Adding to the COVID requirements was an announcement by Bahamas Prime Minister Hubert Minnis last week, mandating all cruise passengers 12 and older to show proof of vaccination for entry into the country from Sept. 3 through Nov. 1.

At least 48 crew aboard the Costa Atlantica cruise ship docked at a port in Nagasakia have tested positive for coronavirus
A cruise ship is pictured. JIJI PRESS / STR