The U.S. Centers for Disease Control and Prevention (CDC) advised against cruise travel for all Americans on Thursday, regardless of an individual's vaccination status.

This decision was made in the wake of a recent increase in positive COVID cases, especially on ships, with the Omicron variant impacting both the unvaccianted as well as those fully vaccinated. Cruise ships that have been running through the United States announced around 5,000 COVID cases to the CDC between the dates of Dec. 15-29, which has been a major increase as compared to the initial part of the month, with only 162 positive COVID cases.

"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 CDC reported.

This advisement from the CDC is a huge disappointment for the cruise industry, since it was so heavily impacted throughout the first year of COVID-19. Stocks of Royal Caribbean Cruises (RCL  ), Norwegian Cruise Line (NCLH  ), and Carnival (CCL  ) all dropped on the news.

The CDC additionally gave warnings that COVID very easily passes on among individuals who are in close proximity to one another on ships, and the chances of catching COVID on the ships is very strong, even for those who are vaccinated.

Some of the other admonitions that the CDC gave are that people who choose to go on a cruise should make the decision to get vaccinated, and that masks ought to be put on, especially in enclosed spaces. Those who choose not to get vaccinated should quarantine for about five days after travel, according to the CDC.

Brian Salerno, senior vice president for maritime policy at Cruise Lines International Association, was very much disappointed with the CDC's choice as the travel industry continues to be impacted by the ongoing pandemic. "We're obviously disappointed at the CDC's decision to raise the travel level for cruise today-especially given the overwhelming level of effectiveness of cruise protocols that are resulting in significantly lower level of cases on cruise as compared to land," Salerno said in a statement regarding the CDC's decision.