Cruise lines have been hunched over on the starting blocks for a long time. And it's only getting worse. Norwegian Cruise Line Holdings (NYSE:NCLH) announced on Tuesday that it is canceling all sailings through the end of March. Its business will have been suspended for more than a year when cruises resume in April – and naturally the restart date could get pushed out again.

It's been exactly two months since the Centers for Disease Control and Prevention (CDC) replaced its "No Sail Order" with a "Conditional Sail Order" that paved the way for a return to cruising for U.S. passengers. Investors initially cheered the news, sending shares of Norwegian Cruise Line and larger rivals Carnival (NYSE:CCL)(NYSE:CUK) and Royal Caribbean (NYSE:RCL) higher, but reality hasn't been as kind.

Instead of rushing to fulfill the new guidelines it seems as if the country's three leading cruise lines are riding out the storm. With now two viable vaccines on the market are Norwegian Cruise Line, Carnival, and Royal Caribbean just waiting for enough of its fan base to be vaccinated? Cruise lines requiring proof of vaccination records before letting passengers sail again may seem outrageous, but it may not be as far-fetched as you think.

Sailing into the big blue unknown

The CDC's conditional framework is rigid. Expanding on-board testing labs and stiff restrictions on what passengers and crew members can do on cruises isn't going to make the experience as bon a voyage as folks remember. Keeping shore excursions on a short leash and perpetual testing regimens in place doesn't sound very inviting. An important stipulation is that each ship would have to go through a series of simulated cruises before receiving regulatory clearance.

Here we are -- two months later -- and it doesn't seem as if any cruise line is launching the series of simulated sailings to prove that they can comply with the new measures. In the meantime we're now seeing the first wave of U.S. citizens receive the first of two COVID-19 shots. Medical specialists on the front line had first dibs on the vaccination efforts, but now the priority has shifted to senior citizens.

The requirements for a "phased resumption" of cruise ship passenger operations were released by the US Centers for Disease Control and Prevention
The requirements for a "phased resumption" of cruise ship passenger operations were released by the US Centers for Disease Control and Prevention AFP / CHANDAN KHANNA

In Florida – where all three cruise ships have their corporate offices and where many of its popular ports are – a governor order last week clears anyone 65 or older to receive the vaccine if it's available. Texas is another port-heavy state that has also given senior citizens the green light to get vaccinated.

The average age of a passenger is 47 according to the Cruise Lines International Association, but many of the customers on sailings tend to be retirees with the means to travel. With cruise lines already scaling back on their capacity levels heading into 2021 they could conceivably start filling ships from the pool of vaccinated cruising buffs well before Norwegian Cruise Line's April restart date.

We can't start jumping to assumptions or conclusions without walking the plank first. It would be a controversial move, and there's a good chance that the notion of requiring vaccinations before cruising is either exciting you or agitating you right now.

The CDC hasn't offered guidance on what the requirements would be if everyone on board -- passengers and crew -- had proof of completing the vaccination process. However, it doesn't seem as if the three cruise lines are rushing to complete the battery of obstacles that the CDC established on the eve of Halloween. The industry has been all tricks and no treats.

With cruise lines braced to ramp up their operations gradually as 2021 plays out it wouldn't be a surprise to see a vaccination requirement on the earliest of sailings. If this seems insane, keep in mind that Norwegian Cruise Line was requiring everyone over 70 to prove their medical fitness -- with a doctor's note -- in early March before it had no choice but to shut down. If the key to a healthy recovery is limiting sailings to healthy vaccinated customers, don't put it past Norwegian Cruise Line, Royal Caribbean, and Carnival to do exactly that to get going again.

This article originally appeared in the Motley Fool.

Rick Munarriz has no position in any of the stocks mentioned. The Motley Fool recommends Carnival. The Motley Fool has a disclosure policy.