A cruise line in the U.K. has added a strict new requirement for passengers looking to set sail: COVID-19 immunization.

Saga Cruises, a UK-based boutique cruise company that advertises largely to older travelers, announced on Wednesday that all passengers be fully vaccinated at least 14 days prior to boarding its river cruises or ocean-going cruises, beginning with the first voyage scheduled for its return-to-service on May 4.

The line previously planned to resume cruising with an April 3 voyage, but canceled the itinerary — as well as those leading up to May 4 — upon announcing the new requirement.

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The Saga Group, which also operates holiday packages including hotels and tours, will also be suspended until at least May 1.

Those booked on river cruises or tours prior to those dates will be contacted by Saga to "discuss their options," Saga wrote.

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"I know how disappointing this news will be for many of you, but I also hope that you will understand why we have made this decision," wrote Saga Holidays CEO Chris Simmonds in a message to affected guests.

In announcing the COVID-19 vaccine mandate, Saga Cruises also appears to be leading the global cruise industry in such a requirement. As for U.S.-based cruises, the CDC has mandated that cruise lines provide a "framework" for conditional sailing, to demonstrate adherence to a health and safety checklist, before resuming sailings.

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Saga’s new vaccination requirements come in addition to its previously announced health and safety protocol for upcoming cruises, including mandatory COVID-19 testing (at home or in the terminal, prior to departure), temperature checks, reduced capacity, social-distancing measures, extra medical staff on ships, and table-service dining options as opposed to buffet, among others.