American Cruise Lines, a Connecticut-based operator of smaller cruises and riverboat cruises, has temporarily mandated that passengers are vaccinated against the coronavirus on all of its sailings. 

A spokesperson confirmed the temporary safety protocol to Fox News on Wednesday. 

"Currently, COVID-19 vaccination is required for all guests for all sailings departing on March 13, 2021, through April 10, 2021, at this time," American Cruise Lines said in a statement. The spokesperson also said that all passengers will be required to take a COVID-19 test within 4 days of the start of their trip.

Though the coronavirus test requirement is listed on the cruise line's website, the vaccine requirement is not. In fact, the American Cruise Lines’ website says passengers may be required to provide two negative COVID-19 test results, one four days before their journey and another on the day of boarding, "if necessary."

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The website also says: "Guests are strongly encouraged to get a COVID-19 vaccine prior to travel." But it does not specify that vaccines are required for current cruises.

American Cruise Lines' modern riverboat American Harmony, pictured. (American Cruise Lines)

Even with the vaccine, passengers will still have to provide negative tests and wear masks, the website added. 

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American Cruise Lines’ website is clear that its safety protocols are "subject to review and change at any time" and that requirements "may vary depending on the region and dates of travel."

American Cruise Lines' coastal cruise ship Independence (pictured), made its first departure of 2021 earlier this month.  (American Cruise Lines)

"We are regularly communicating with all guests regarding any additional testing, vaccination, and shoreside operating requirements that may be necessary given the region and time period of their travel," the cruise line says on its website.

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According to review website Cruise Critic, some passengers were unaware of the cruise line’s temporary vaccine requirement until this weekend, just before American Cruise Lines’ new riverboat, American Jazz, launched on Sunday. 

In a statement provided to Cruise Critic, an American Cruise Lines spokesperson said that passengers who were affected by the change in policy were offered a full refund or a chance to sail on a different cruise later this year.

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American Cruise Lines launched its first cruise of 2021 earlier this month. 

The cruise line’s fleet of 13 riverboats and coastal cruise ships run on the smaller side, holding between 100 and 190 passengers. Currently, the CDC's Conditional Sail Order only prohibits commercial vessels from operating in U.S. waters if they have the capacity to carry over 250 individuals.