The Centers for Disease Control and Prevention issued a new advisory Thursday that travelers should avoid traveling by cruise ship, regardless of vaccination status, after a recent surge in positive COVID-19 cases onboard ships.

The agency increased its travel warning for cruises to Level 4 — the highest level — following investigations of dozens of ships that have had outbreaks of the virus.

“Even fully vaccinated travelers may be at risk for getting and spreading COVID-19 variants,” the CDC said on its website…

“It is especially important that travelers who are at an increased risk of severe illness from COVID-19 avoid travel on cruise ships, including river cruises, worldwide, regardless of vaccination status,” the agency added.