COVID-19 is spreading on cruises again. This time, they plan to keep sailing.

The cruise industry thought it had adapted to covid-19. After emerging from a 15-month shutdown with a slew of new regulations approved by the Centers for Disease Control and Prevention, ships got back on the water in late June. Carnival CEO Arnold Donald said in a December earnings call that the company had established “effective” protocols for the 65,000 workers and 50 ships back in operation.

Now, though, the omicron variant of the coronavirus has changed the climate. Through Tuesday, 86 cruise ships carrying passengers in U.S. waters were reporting coronavirus cases onboard, the most since the comeback, according to CDC tracking data.

Over the past week of holiday travel, stories of outbreaks, customers isolating in their cabins and ports turning away ships evoked conditions that brought cruising to a halt in March 2020, albeit without the severe cases or deaths that marked the first wave of the pandemic. Cruise lines have imposed stricter measures since the omicron variant’s discovery, and no industry-wide pause appears to be in sight.

When reached by The Washington Post this week, the CDC said it plans to allow its Conditional Sailing Order to expire as planned on Jan. 15. At that point, the restrictions imposed for pandemic-era cruising will become recommendations.

“CDC acknowledges that it is not possible for cruising to be a zero-risk activity,” the agency said in a statement this week. “The chance of getting covid-19 on cruise ships is high because the virus spreads easily between people in close quarters aboard ships.”

In light of the most recent outbreaks, at least one lawmaker is calling for a second shutdown on cruises.

“Time for CDC & cruise lines to protect consumers & again pause - docking their ships,” Sen. Richard Blumenthal, D-Conn., tweeted Tuesday. “Cruises are repeating recent history as petri dishes of COVID infection.”

The steep rise in passenger ships with cases onboard - up from 73 on Monday - is a result of a couple of factors: Cruise lines are returning more ships to service, and the omicron variant is tearing through the population on land.

Cruise companies restarted U.S. trips in the summer with strict protocols they said should give passengers peace of mind. Those measures evolved - especially after the emergence of the delta variant in late summer - to include coronavirus vaccine requirements for most or all passengers, pre-cruise testing and masking in some crowded indoor areas, even for the vaccinated.

Omicron is forcing them to adapt as the highly transmissible variant causes the largest outbreaks the industry has seen in the United States since last year. But unlike 2020, when cruising shut down worldwide, the industry is not in a tailspin. Most of the recent infections detected onboard have been mildly symptomatic or asymptomatic, according to operators and the CDC.

“I think they’re in better shape than spring 2020,” said Andrew Coggins, a professor at Pace University who teaches cruise industry management. “Much more is known about covid, and we have testing, vaccines and protocols.”

Cruise lines say they are reacting to the omicron variant with additional requirements, namely mask rules indoors for everyone unless they are eating, drinking or in their own staterooms.

MSC Cruises said Tuesday that it will add - and pay for - an additional antigen test for all new passengers, either as they are boarding or once they’re onboard.

“The new testing measure is part of our comprehensive protocol, which is designed to adapt its measures in line with the evolution of the pandemic ashore,” the company said, adding that this includes the current surge and omicron’s rise as the dominant variant in the United States.

Some lines, including Carnival, are prohibiting smoking in casinos in the near term. And while many are encouraging passengers to get a coronavirus booster shot, they are not mandating it. The world’s biggest cruise lines, Carnival and Royal Caribbean, said crew members are getting boosters once eligible.

Bari Golin-Blaugrund, spokeswoman for Cruise Lines International Association, said in an email that the industry’s measures include a focus on providing medical care, contact tracing, isolating potential cases and other efforts to keep cases from spreading.

In response to Blumenthal’s tweet Tuesday, Golin-Blaugrund said that cases on ships in recent weeks made up just a small percentage of the populations onboard and that no setting is immune from the virus.

The CDC is investigating dozens of cases on cruise ships and advising cruise lines to require masks indoors and outside in crowded areas.

Infectious-disease experts say the rules that cruise lines have in place are very good - but not perfect.

An infected passenger might not have enough virus to show up in a pre-cruise test but could become symptomatic during a trip, said William Schaffner, professor of preventive medicine and infectious diseases at Vanderbilt University School of Medicine in Nashville.

“With a virus that’s so contagious as omicron, it can wriggle its way through some of these barriers that we put up,” he said. “And in a rather contained population where people have intensive face-to-face contact all the time, that’s an ideal environment for a virus like this to spread.”

Gigi Gronvall, a senior scholar at the Johns Hopkins Center for Health Security, said testing for more than one day in a row would be wise before passengers board. She said she was glad to see at least some cruise lines, including Disney, requiring children as young as 5 to be vaccinated.

Thomas Russo, professor and chief of the division of infectious diseases at the University at Buffalo, had a Baltic cruise planned for this August and September that he postponed a year because of ports closing and logistics concerns.

He said that although he enjoys cruises, now is not the time for anyone who is immunocompromised or at high risk of severe disease - advice the CDC also gives.

“I think it’s a hard pass on cruises right now” for that population, he said. “Just be patient, wait until this current wave passes.”

Jessica Justman, an infectious-diseases specialist and epidemiologist at Columbia University, has a family member on a Caribbean cruise now.

“We talked about how breakfast and lunch were meals that could be eaten outdoors on the deck,” she said. “So the only time where you have to eat indoors is at dinner.” She suggested eating that meal quickly and then putting a mask right back on.

Justman said if she were considering a cruise, she would want one that mandated vaccination and boosters for everyone, as well as testing twice a week.

So far, cruise companies and observers say they are seeing some short-term cancellations in light of the omicron surge, but solid longer-term demand has persisted.

Colleen McDaniel, editor in chief of Cruise Critic, said members of her site’s active online community are “reevaluating” what they want to do.

“What we’re seeing right now is pretty substantial discussion about it,” she said. Some plan to still go, others are planning to reschedule until the summer.

McDaniel said most have concerns: “Am I going to have fun on a cruise? Am I going to be OK if I have to wear masks in public? Am I going to be able to return easily to the United States? Am I going to get turned away from the port I want to visit?”

Ilana Schattauer, a cruise travel blogger from Montreal who runs the website and YouTube channel Life Well Cruised, posted a video Sunday about her own upcoming cruise. She leaves Fort Lauderdale, Fla., on Wednesday on Regal Princess for an eight-day Caribbean cruise with her husband and 21-year-old son.

“Our biggest concerns are being stuck on the ship or testing positive, even if we are asymptomatic or have mild symptoms,” she said in an email. “We realize that this new variant is so contagious, and even being fully vaccinated we still have a risk of being exposed. We also need to head back to Canada after the cruise, which is another complication.”

Still, Schattauer said she didn’t want to cancel. She feels comfortable with the cruise line’s mask policy and other safety measures.

“Hopefully with the stricter protocols and mask rules, we’ll see less cases than we’ve seen on a few cruise ships that have recently been in the spotlight,” she said.