In a major win for cruise fans, the U.S. Centers for Disease Control & Prevention updated its Conditional Sailing Order on May 12 to loosen mask-wearing requirements for fully vaccinated cruise passengers.

The update also allows vaccinated cruise passengers to explore independently on shore at ports of call.

The CDC also indicated that there would be more changes, a spokesperson for the body told Cruise Critic: "Additional updates to the cruise guidance are coming soon."

In the updated rules for the resumption of cruises, the CDC says cruise ship operators "at their discretion, may advise passengers and crew that -- if they are fully vaccinated -- they may gather or conduct activities outdoors, including engaging in extended meal service or beverage consumption, without wearing a mask except in crowded settings."

The CDC further says cruise lines may allow fully vaccinated passengers to explore ports on their own. The agency says those who are vaccinated "may engage in self-guided or independent exploration during port stops, if they wear a mask while indoors."

The CDC notes, however, that foreign countries could have their own requirements concerning independent port exploration.

Immediately, lines began putting out information. Masks will not be required at Royal Caribbean's private island, Perfect Day at CocoCay, Vicki Freed, the line's senior vice president of sales, said in her Wednesday Coffee Talk.

And Norwegian Cruise Line Holdings released the following statement:

"The U.S. Centers for Disease Control and Prevention (CDC) recently provided modifications to previously issued technical guidance under the Framework for Conditional Sailing Order (CSO). We continue to work with the CDC to establish an agreeable path to the safe resumption of cruising in the U.S. while protecting guests, crew and the communities we visit."

The CDC has been meeting frequently with cruise lines since it updated its guidance for test cruises and restricted startup cruises last week. The updates included rules for mask wearing, social distancing and shore excursions.

Cruise line officials, including Frank Del Rio, president and CEO of Norwegian Cruise Line Holdings, had criticized the agency for not issuing separate guidance for passengers who are fully vaccinated, as opposed to those who are not. Norwegian Cruise Line has committed to sailing ships with 100 percent vaccinated passengers and crew through October.

Cited as particularly onerous in the original guidance were restrictions on how long cruise passengers can take off their masks to dine, as well as rules to wear a mask outdoors by the pool. The updates appear to address some of these concerns.

At a White House news conference Thursday, CDC Director Rochelle P. Walensky said Americans who are fully vaccinated may stop wearing masks and social distancing in most indoor and outdoor spaces. There are exceptions to the new guidance including when traveling by bus, plane, train and other modes of public transportation. It was unclear how this could affect the agency's cruise guidance.