The CDC released relaxed travel guidelines for vaccinated Americans on Friday, but before boarding your next cruise, you may need to show proof that you received the COVID-19 vaccine.

Erika Behlmer-Rothberg, a 30-year-old Ph.D student from Florida, has finally booked a honeymoon with her husband. She chose a European river-cruise vacation for the week of Christmas as a honeymoon getaway with her husband. She’s in favor of cruise lines requiring vaccines.

“We had put a pause on both our wedding and honeymoon planning until my husband and I got our first doses, because we wouldn’t even dream of leaving the house prior to the vaccine, let alone travel,” Behlmer-Rothberg said.

She and her husband have thought their decision through. “River cruises are a fraction of the size of a major ocean liner,” she said, “so that already limits our exposure.”

The pandemic even informed the couple’s choice of cruise vacation: a river cruise through Germany and the Czech Republic.

“These cruises are usually attract a much older crowd, who I imagine were considered priority in their states for vaccinations,” Behlmer-Rothberg said.

She and her husband will be traveling on Viking River Cruises. The company did not respond to a request for comment.

Viking River Cruises has not announced a vaccination requirement for its upcoming sailings, but the company plans to require daily PCR COVID tests — regarded as the gold standard among coronavirus tests — for guests and crew on its ships to prevent outbreaks of the virus.

Early in the COVID-19 pandemic, some of the most prominent clusters occurred on cruise ships. In the months that followed, many countries prohibited ships from docking because of concerns about the virus’ spread. Other cruise lines had deaths from the coronavirus on board and, as the industry suspended services, shares of cruise lines plummeted.

Behlmer-Rothberg may be surprised at the average age of a cruise passenger. It hovers at just under 47 years old, according to the Cruise Lines International Association Global Passenger Report.

Saga Cruises, based in England that caters to travelers over the age of 50, was among the first to announce a vaccination requirement.

However, 40 to 49-year-olds account for approximately 15% of all cruise passengers for that year. The median age range was between 60 and 69 years old, accounting for 19% of cruise passengers.

On April 2, the U. S. Centers for Disease Control and Prevention unveiled new travel guidelines for people vaccinated against COVID-19. The public health agency said that vaccinated Americans could travel domestically without getting a COVID-19 test or self-quarantining. International travelers who are vaccinated are still encouraged to get a negative COVID-19 test before returning to the U.S. from abroad, but they don’t need to stay home upon their return if they took precautions during their trip.

The agency, however, has maintained its recommendations against travel because of new variants of the virus, which the vaccines may not protect against.

Even before the CDC’s new guidelines came out, multiple cruise lines have rolled out their own requirements for passengers to be vaccinated before sailing. Saga Cruises, a cruise line based in England that caters to travelers over the age of 50, was among the first to announce a vaccination requirement for its passengers.

Back in January, the cruise line announced that guests must be fully inoculated before their trip — meaning that they must have received both of the doses of the COVID-19 vaccine at least 14 days before sailing.

In recent weeks, a growing number of cruise lines have followed suit and rolled out their own policies stipulating that guests over the age of 18 be vaccinated. Some cruise lines have opted to require this only for specific sailings at this time, while other cruise lines like Virgin Voyages have introduced the mandate for all their upcoming itineraries.

“Our goal is to ensure that we’re providing the safest travel experience which means vaccinations for both our crew and passengers,” Virgin Voyages CEO Tom McAlpin said in announcing the cruise line’s vaccine requirement.

Some of the cruise lines that have mandated vaccines are targeting specific markets where the vaccine rollout has been successful.

Norwegian Cruise Line NCLH, -2.20% is the latest to introduce a vaccine requirement. The cruise line said it plans to resume operations this summer, starting with sailings out of Jamaica, Dominican Republic and Greece in July. The company has said its initial trips will only allow “fully vaccinated guests and crew,” and those who travel will be required to get tested for COVID-19 before boarding the ship.

“We are exploring all options regarding vaccinations for guests and crew, and it is our intention that all crew members be vaccinated before boarding our vessels to begin their duties, subject to availability of the vaccine,” a spokesperson for Norwegian Cruise Line NCLH previously told MarketWatch.

Royal Caribbean International RCL, -1.37% also requires all passengers and crew for its initial voyages to be vaccinated, a spokeswoman said.

Some of the cruise lines that have mandated vaccines are targeting specific markets where the vaccine rollout has been successful. Both P&O Cruises and Princess Cruises are booking cruises around the coast of the United Kingdom that are limited to U.K. residents who have been vaccinated.

The U.K. has approved the two-shot vaccines developed by Moderna MRNA, +1.83% and Pfizer-BioNTech PFE, +0.14% BNTX, +1.03% as well as the one-shot vaccine developed by AstraZeneca AZN, +2.23% and Oxford University.

“Our decisions will be informed by our global medical and science experts and requirements of the places we operate and visit,” a Carnival Corp. CCL, -1.52% spokesperson said in a statement to MarketWatch. “There may be some brands, like P&O Cruises in the UK, that initially require vaccinations based on select ships and country-by-country requirements.”

In cases where vaccines are required, guests can generally just show the original documents they received at the time of their shot.

Because the vaccines have not been approved in children yet, younger passengers must instead provide proof of a negative COVID-19 test prior to boarding in cases where they are allowed on the ship.

Erika Behlmer-Rothberg, and her husband Dustin, pictured during a previous trip to London. The couple is planning to take a river cruise in December for their honeymoon.

Industry responds to public pressure

The decision by cruise lines to mandate the COVID-19 vaccine in part may reflect the various approaches different countries have taken toward international travel.

“Several countries, such as Greece and Iceland, are requiring vaccines for international travelers, so any cruises that eventually sail or visit those ports will have to follow those requirements,” said Chris Gray Faust, managing editor of travel website Cruise Critic. “We could see more of that from destinations across the globe.”

But cruise lines are likely also responding to the desires of travelers. P&O Cruises, in announcing its U.K. sailings that feature a vaccine requirement, cited the “strong expressed preference” among its customers that the upcoming itineraries be limited to people who are vaccinated.

A recent survey of more than 2,000 people from Cruise Critic indicated that vaccine requirements are extremely popular. In the poll, 85% of people said they would take a cruise if people were required to be inoculated against COVID-19 in advance, versus just 7% who said they would not sail if such a policy were in place.

Cruise lines have yet to resume operations from American ports as they work to comply with new requirements laid out by the Centers for Disease Control and Prevention.

Cruises are not sailing out of America

For cruise operators that sail out of America, how to approach vaccinated passengers will be one part of the puzzle of resuming operations.

Last fall, the U.S. Centers for Disease Control and Prevention chose not to extend the no-sail order put in place earlier in the COVID-19 pandemic. Instead, public-health officials rolled out a series of requirements that cruise operators would need to meet to resume sailings as part of a conditional sail order.

Since the new requirements were first announced, no company has begun sailing from U.S. ports yet — travel experts have warned it would take the cruise lines months to return given the challenges involved.

Currently, cruise lines are expected to run the required test sailings as part of the CDC’s new protocol in June or July, “if a cow jumps over the moon and planets align,” said Stewart Chiron, a travel expert who runs The Cruise Guy website.

Cruise lines have resumed operations out of other countries, particularly in Europe and Southeast Asia. In some cases, passengers onboard these ships have tested positive for COVID-19.

“COVID-infected passengers will inevitably get onboard and it’s how cruise lines mitigate the situations, minimize inconveniences and disruptions, that makes the difference,” Chiron said.

In spite of this possibility, Chiron argued that vaccine requirements may be premature. “There’s no point to making such announcements right now as the situations is so volatile,” he said.

For cruises to resume sailing out of ports across the U.S., it will take a combination of factors beyond the nation’s vaccine rollout. Cruise lines will still need to develop processes around COVID testing, temperature checks and social distancing.

“It’s going to be a combination of a lot of protocols, procedures and technology that will be used not only for the cruise industry but for many others,” he said.

Behlmer-Rothberg, meanwhile, is excited for her honeymoon cruise. It has, after all, been a long time coming. She is happy with her choice of honeymoon, and remains unfazed by previous stories of cruise-ship outbreaks.

“We are so excited to go on vacation after quarantining for so long,” she said. “We had to postpone not just our honeymoon, but the giant wedding that we had planned last year, so we’re so excited to finally celebrate our marriage with our loved ones.”

“One of the best things about cruising is that you can go to sleep in one city (or country) and wake up somewhere entirely different, so after a year-plus of no travel, being able to visit so many locations in one trip is especially exciting,” she added.

“We can’t wait.”

Which cruises lines are requiring vaccines?

American Queen Steamboat Company and Victory Cruise Line All passengers and crew members (including employees on- and off-ship) are required to be vaccinated prior to embarkation.
Carnival Corp. (Lines include Carnival, Costa Cruises, AIDA) Some brands may initially require vaccinations for select ships or based on specific countries’ regulations.
Celebrity Cruises Vaccines will be required initially for all adult guests, while children under the age of 18 must have a negative PCR COVID-19 test result within 72 hours of embarkation.
Crystal Cruises All guests are required to be fully vaccinated at least 14 days prior to boarding, with proof of vaccination presented at boarding.
Holland America Line Vaccines are not yet required.
Norwegian Cruise Line Vaccines are not yet required for passengers, but the company intends to have all crew members vaccinated prior to boarding Norwegian’s vessels.
P&O Cruises (A Carnival Corp. subsidiary) For a series of sailings along the U.K. coast, all guests must be U.K. residents who are vaccinated.
Princess Cruises For a series of coastal U.K. sailings, only fully-vaccinated, U.K. residents will be allowed to travel. Proof of vaccination will be required.
Royal Caribbean International As Royal Caribbean begins sailing again, all adult guests and crew are required to be fully vaccinated before boarding. The original, standard vaccine verification issued by the home country’s health aithority will suffice as proof, including the CDC card.
Saga Cruises All guests must be fully vaccinated, having received both doses of the COVID-19 vaccination at least 14 days before traveling.