Omicron’s ubiquity and reduced severity are encouraging some people to drop pandemic precautions, decisions that public-health experts say present new risks for people at risk of severe Covid-19 outcomes.

People, including those who got vaccinated and boosted and curtailed their activities for months, are letting their guard down in the face of a variant that appears to be infecting everyone but causing largely mild illness.

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Omicron’s ubiquity and reduced severity are encouraging some people to drop pandemic precautions, decisions that public-health experts say present new risks for people at risk of severe Covid-19 outcomes.

People, including those who got vaccinated and boosted and curtailed their activities for months, are letting their guard down in the face of a variant that appears to be infecting everyone but causing largely mild illness.

This is a dangerous way of thinking, doctors and scientists say: Omicron still poses risks to more vulnerable people, including the elderly, immunocompromised and those with underlying health conditions. Some doctors say they are also worried about Omicron resulting in more long-Covid cases, which can result in lingering and worsening symptoms months after infection, as well as questions of new variants arising with such widespread infection.

The Centers for Disease Control and Prevention encourages people to avoid nonessential travel and eating inside restaurants. But some people say that they are tired of waiting to reconvene with other people and the world, and that they believe the risks of the pandemic have declined.

Joseph Anderson, a 39-year-old librarian in New York City, said he spent the past two years doing everything he could to protect himself and others. He followed CDC guidelines and got Covid-19 vaccinations as soon as they were available. In December, Mr. Anderson, his wife and 11-month-old son all contracted Covid-19 and spent Christmas in isolation with mild, flulike symptoms. He and his wife considered canceling their son’s first birthday party this past Saturday, but after recovering from Covid-19, they chose not to hold back.

“When you’re scared about something for so long and then it finally happens, you kind of feel almost a sense of relief,” he says.

Joseph Anderson and his family spent Christmas in isolation with mild, flulike Covid-19 symptoms.

Photo: Amir Hamja for The Wall Street Journal

Mr. Anderson plans to socialize and travel sooner rather than later, while his immunity from his vaccinations and recent infection is likely to be the strongest. He is planning a family trip to see his brother in New Orleans.

“I kind of feel like after getting vaccinated and boosted and contracting it that I’m as protected as I can possibly be as a person right now,” he says.

Karen Edwards, an epidemiologist at the University of California, Irvine, says the threat of Covid-19 means you should avoid eating and drinking in public if you can. More interactions between potentially infected people will give the virus more pathways to spread and potentially mutate, she says.

“If we had a variant that caused severe disease like Delta and was as transmissible as Omicron, we wouldn’t want to see that,” Dr. Edwards says.

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More transmission also threatens immunocompromised people, Dr. Edwards says. “They may be vaccinated and boosted and because of their underlying disease or medications they’re taking, their immune system is not going to react in the same way that a healthy individual’s would,” she says.

Anyone who is infected can transmit Covid-19 to people for whom Omicron might present more of a threat without knowing it, says Michael Lin, an infectious-disease physician at Rush University Medical Center in Chicago.

“It’s not mild to moderate for everybody,” Dr. Lin says.

Eman Rimawi-Doster, 37, who has lupus and had one leg amputated above the knee eight years ago, said she lives every day anxious that she will catch Omicron.

“I don’t want to be a victim of Covid, and there’s no way for me to prevent it except to stay in the house,” says Ms. Rimawi-Doster, who works for a nonprofit civil-rights law firm in New York City.

Eman Rimawi-Doster, who has lupus, said she is concerned that she will catch the Omicron variant.

Photo: Amir Hamja for The Wall Street Journal

Ms. Rimawi-Doster, who is fully vaccinated and boosted, said she has lost some three dozen friends to Covid-19, some of whom didn’t have pre-existing conditions.

“If completely healthy people are dying from this, what chance do I have?” Ms. Rimawi-Doster says. “People don’t think that disability is something that will ever affect their lives personally. But anybody can join the club at any time.”

Another reason to avoid Omicron, doctors say, is that with previous variants, even mild to moderate cases sometimes resulted in long Covid, which is when people experience persistent and often worsening symptoms after an infection.

Long Covid affects roughly 10% to 30% of people with Covid-19, research suggests. Also sometimes called long-haul Covid, it has been associated with symptoms including cognitive problems, extreme fatigue, a racing heart rate and shortness of breath that can last for many months and even years.

While it is too early to know if Omicron will generate a whole new set of long Covid patients, experts say there is no reason to think it won’t.

Joseph Anderson plans to socialize and travel sooner rather than later, while immunity from his vaccinations and recent infection is likely to be the strongest.

Photo: Amir Hamja for The Wall Street Journal

“The majority of our patients in the long-haul clinics had very mild illness to begin with,” says Greg Vanichkachorn, an occupational and aerospace medicine physician at Mayo Clinic in Rochester, Minn., who works with long Covid patients in the first three months after their infection. “One of my greatest fears is that these patients that are now experiencing these mild cases may go on to have long-haul Covid. If that is the case with so many people getting sick, we could have this tsunami of long-haul cases in a few weeks or months.”

Dr. Vanichkachorn says the clinic has seen a few patients infected with Omicron who are struggling with symptoms about three weeks after their initial infection. He recommends that if patients haven’t recovered two or three weeks after an infection they should seek medical care.

Eddie Stenehjem, an infectious-diseases doctor at Intermountain Healthcare in Utah, understands why people are yearning to live a post-Covid life but warns that it is too soon. Without clinical studies and extensive data, it cannot be determined that prior infection to Omicron is going to be protective against other variants of concern like Delta, Dr. Stenehjem says.

“We need to make sacrifices right now to protect the vulnerable population,” Dr. Stenehjem says.

Misha Mutizwa, a 38-year-old dermatologist in the Philadelphia area, believes people with different risk profiles should adopt different behaviors, while Omicron is circulating. He hasn’t had Covid-19, is fully vaccinated and boosted and feels comfortable living most of his life as he did before the pandemic.

“We should have options available for those of us who are ready to safely and thoughtfully start to transition back into a relatively normal life,” Dr. Mutizwa says.

As a physician, Dr. Mutizwa wears masks at work and other places they are required. But he has been traveling for leisure and doesn’t plan on slowing down. He selected Panama as a recent destination, in part because of the country’s high vaccination rates.

“I think at some point we have to move forward as a society because this idea of indefinite masking and restrictions on folks is psychologically burdensome,” Dr. Mutizwa says.

Write to Sumathi Reddy at sumathi.reddy@wsj.com