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The "Seven Seas Mariner" cruise ship traveling from Florida passes through the Panama Canal after it was barred from docking by local authorities in Cartagena, Colombia, on Wednesday due to COVID-19 infections on board, on the outskirts of Panama City, Panama.

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"Since the identification of the Omicron variant, there has been an increase in the number of COVID-19 cases among cruise passengers and crew reported to CDC. Additionally, there has been an increase in the number of cruise ships meeting the COVID-19 case threshold for CDC investigation," the agency said.

"The decision by the CDC to raise the travel level for cruise is particularly perplexing considering that cases identified on cruise ships consistently make up a very slim minority of the total population onboard -- far fewer than on land -- and the majority of those cases are asymptomatic or mild in nature, posing little to no burden on medical resources onboard or onshore," CLIA said in a statement.

The association said that "cruise ships offer a highly controlled environment with science-backed measures, known testing and vaccination levels far above other venues or modes of transportation and travel, and significantly lower incidence rates than land."

While the CDC says to "avoid cruise travel, regardless of vaccination status," it advises those who do travel on a cruise ship to make sure they are fully vaccinated and boosted, if eligible. People who go on a cruise should also get tested one to three days before their trip, and three to five days after, regardless of vaccination status.

Most cruise lines are requiring all or the vast majority of passengers and crew to be vaccinated, in compliance with a CDC Conditional Sailing Order that was implemented to allow cruise operations to resume more than a year after the industry came to a standstill at the start of the pandemic.

CNN's Jason Hanna contributed to this report. Top image: The Seven Seas Mariner cruise ship passes through the Panama Canal on December 23 after it was barred from docking by local authorities in Cartagena, Colombia. (Reuters/Erick Marciscano) 041b061a72