Six months ago, the big question cruise stocks investors were asking was this: When will ships sail once again from U.S. ports? As more and more people lined up for coronavirus vaccination, there was reason for optimism. Vaccinations would help stop the pandemic -- and open the door to cruising once again. As a result, Carnival (CCL 0.67%) (CUK 0.74%) shares climbed nearly 45% from January through early June.

Then came the moment we've all been waiting for. This summer, Carnival's ships resumed North American operations. And the company has big plans for the rest of the year. At the same time, the shares have stagnated. Let's take a closer look at the situation -- and at why everyone is talking about Carnival stock right now.

Adult and child smile and lean against the railing of a cruise ship at sea.

Image source: Getty Images.

The high point

So first, a bit about share performance since this year's high point, reached on June 2. The stock has since slipped more than 20%. Shares fell as the highly contagious delta variant gained ground. And coronavirus cases -- which had dropped earlier in the year -- soared once again. Even with ships sailing, investors worried demand for cruise vacations would suffer.

Now, getting back to the latest Carnival news. In July, Carnival Cruise Line ships sailed from Texas and Florida for the first time in about 16 months. And Carnival's Princess and Holland America lines resumed cruises from Seattle to Alaska. Some of the companies' European brands -- such as Costa Cruises -- already had resumed sailing in the spring. The world's biggest cruise operator said it expects to return 65% of its fleet to the seas by the end of the year.

Of course, cruising today isn't the same experience as cruising pre-pandemic. A look at Carnival Cruise Line's "Have Fun. Be Safe." page details the safety measures. Vaccination is required for most passengers. There are exemptions for children under age 12 (there isn't an authorized vaccine available for this age group yet). And there are exemptions for adults with certain medical conditions. These unvaccinated passengers are only allowed to visit ports of call if they purchase a "bubble tour." This sort of shore excursion is escorted directly to and from the ship and happens in a controlled environment.

Vaccinated and unvaccinated passengers must wear masks in most indoor areas of the ships. And all guests are required to present negative coronavirus test results before boarding.

The best efforts

These measures sound like good ways to halt the spread of the coronavirus. But so far, even the best efforts haven't been enough. One of Carnival's ships sailing out of Texas this summer reported 27 cases in a two-week period, according to a CNBC report. That's the biggest outbreak since cruising resumed.

At the same time, on Aug. 20, the Centers for Disease Control and Prevention (CDC) recommended that high-risk individuals should avoid cruises -- whether they're vaccinated or not.

So, what does all of this mean for investors? Well, we have some good news here and some bad news. The good news, of course, is that sailing has resumed. And future demand looks positive. In the most recent earnings report, Carnival said advanced bookings for 2022 cruises were "ahead of a very strong 2019."

That tells us people want to go on cruises -- eventually. Once the pandemic is over and the travel environment is back to normal, I'd expect major demand for cruise vacations.

The cruising we used to know

But here's the bad news: In the coming months, cruising isn't going to be like the cruising we knew before the pandemic. And that means demand probably won't be the same either. For instance, those most vulnerable to the coronavirus may follow the CDC's advice and avoid cruise ships. And others may worry that in spite of the cruise company's efforts, outbreaks still have happened onboard. So, they may opt for another type of vacation.

It's too early to say how long this situation will last. It will be important to follow the rollout of vaccine booster shots. If boosters prove highly effective and coronavirus cases decline for a sustained period, we may see the light at the end of the tunnel. At the same time, it will be important to keep an eye on Carnival's next earnings reports. Resuming operations is great news. But it will also be costly for the company.

It's clear the coming months will be crucial for Carnival. If demand -- and revenue figures in upcoming earnings reports -- pick up, shares may resume gains. But if travelers avoid the seas, Carnival shares may stagnate for a while. In any case, conversation about this cruise line stock is far from over.