UPDATE: Carnival acts...(See below)
Norwegian Cruise Line has gone head-to-head with CDC, asking permission to restart cruises from the U.S. on July 4, with only vaccinated passengers and crew, and a full regimen of cleaning and other safety protocols.
Up to now, CDC has barely moved from its last-March 'no sail order' to an October 'conditional sailing order' whose requirements no line has met because the requirements have still not been issued by CDC, although it has recently said it would say more soon.
Now that CDC has publicly said that travel for fully-vaccinated people is low risk and can resume, cruise lines and cities that depend on cruise business have been growing increasingly restive with CDC's lack of motion on the cruise front.
Most lines that have resumed some cruising are either limiting their passengers and cruises to areas that have a 'bubble,' such as Royal Caribbean's cruises among Israel, Greece and Cyprus, or are limited to residents of one country and have no port calls, such as P&O's 'staycation cruises' in the UK. A few other lines have specified 'vaccinated-only' but with exemption for those under 18 for whom vaccines have not been approved. NCL, however, is going further with a willingness to pass up family groups in favor of an absolute vaccine rule.
NCL is also stationing ships for itineraries that sail out of Montego Bay, Jamaica, Punta Cana in the Dominican Republic and from Athens. Those voyages will also require proof of vaccination.
With cruising from U.S. ports banned for more than a year now, but having a slow revival elsewhere, the 90+% of the industry that sails from the U.S. is growing restive, Other lines that are homeporting ships outside U.S. waters to restart cruising includee Viking, Crystal and Celebrity.