Windstar has confirmed it will require all guests to provide proof of Covid-19 vaccination to sail with the firm "until further notice".
The line said the move was in the best health and wellness interests of guests, crew and those living in the places where the yacht specialist plans to call.
"Many Windstar destinations and some airlines have announced, or are considering, vaccine mandates, providing further support for the new Windstar policy," said the line in a statement.
President Christopher Prelog said vaccination was "another layer of safety" for all, stressing the line’s insistence on vaccination was the "responsible course of action".
"Looking at the science behind the virus, we see consistent recommendations for wearing masks, social distancing, testing, and enhanced cleaning," said Andrew Todd, chief executive of Windstar and parent Xanterra Travel.
Todd added the line’s Beyond Ordinary Care programme ensured "hospital-grade" measures across air filtration, germicidal irradiation and surface sanitisation.
Additionally, Windstar said increased vaccine availability in the US gave it confidence those wishing to sail with the line would have time to be vaccinated before they travel.
President Biden has forecast a greater degree of normality in the US by July, which is when Clia and the US Travel Association is hopeful of a resumption of cruise operations.
Windstar crew will be required to be vaccinated as soon as the vaccine is available to them. The line has also pledged to periodically review its vaccination policy and other Covid guidelines as the pandemic continues to evolve.
It hopes to restart "in a phased manner" in June, with cruises initially operating at reduced capacity with enhanced health and safety protocols.
Star Breeze is scheduled to sail the Caribbean and Wind Star the Mediterranean from 19 June. From 15 June, Wind Spirit will sail from Tahiti, with Wind Surf joining Wind Star on the Mediterranean from 8 August.
Star Legend is due to resume operations in northern Europe from 4 September and Star Pride the Caribbean from 3 November.
Final payment dates have been moved from 120 days prior to departure to 60 days.
Guests will be required to provide proof of a completed vaccine course of one or two shots, depending on the vaccine, with the final dose administered at least 14 days prior to embarkation.
A negative test for Covid-19 will also be required prior to boarding.