Omicron prompts more cruise lines to cancel trips.

The Omicron variant has caused several trips to be canceled by Royal Caribbean International and Celebrity Cruises.

Hundreds of passengers have contracted the coronaviruses onboard ships, with many falling ill and spending days in the hospital.

Royal Caribbean canceled a sailing on the ship Independence of the Seas on Friday due to "covid-related circumstances around the world."

The company said this month that it had called off trips on three ships and delayed the return of another, Vision of the Seas, to March.

Celebrity Cruises said in a statement on Monday that it had delayed service on its ship Celebrity Eclipse. The ship was supposed to make four trips in March and April.

The cruise industry has been hard hit by the Pandemic. It was almost shut down for 18 months before making a comeback this summer, but the industry has recently faced criticism about its safety protocols.

The Centers for Disease Control and Prevention advised travelers to avoid cruises after they were vaccinations. The warning level for cruise ships was raised to 4, the highest level.

The number of ships that have been affected by an outbreak has grown, causing some ports to turn away ships. In December, clusters broke out on two Royal Caribbean cruises after they left port in Florida, and more than a dozen people tested positive on a Norwegian Cruise Line vessel after it returned to New Orleans.

Royal Caribbean and Celebrity Cruises require passengers to receive inoculations. Younger passengers who are not eligible must be tested before sailing.