CHICAGO — With infection rates mounting, the Omicron variant has ushered in a new and disorienting phase of the pandemic, leaving Americans frustrated and dismayed that the basic elements they thought they understood about the coronavirus are shifting faster than ever.

There were reasons for heightened concern and reasons for consolation: Omicron is more transmissible than previous variants, yet it appears to cause milder symptoms in many people. Hospitalizations have soared to new highs in some states, but “incidental patients” — people who test positive for Covid-19 after being admitted for another reason — make up close to half of their cases in some hospitals.

Public health officials, in response to the new variant, have halved the recommended isolation period for people with positive tests to five days from 10 days, while also suggesting people upgrade their masks from cloth to medical-grade when possible.

“Omicron has turned, quickly, into something that is just different,” said Dr. Allison Arwady, Chicago’s top health official.

Amid shifting federal public health guidance and the new and distinct variant, President Biden’s own former transition team has called on the president to adopt an entirely new domestic pandemic strategy geared to the “new normal” of living with the virus indefinitely, not to wiping it out.

And Americans, confronted with these new sets of facts, warnings and advisories, have responded with a mix of confusion, vigilance and indifference. Left mainly to navigate it all on their own, they must sort through an array of uncertain risks — ride a bus? visit friends? eat inside? — hour by hour.

Many people wonder whether they should keep their children home from school or cancel vacations and dinners out. They scramble for at-home antigen tests or appointments for sophisticated P.C.R. tests and are discarding cloth masks in favor of KN95s and N95s. In some cities, they have returned to wearing masks even outside, and are ordering grocery deliveries or stocking up on supplies to avoid trips for the days ahead.

Others have shrugged off the rising cases, focusing on the encouraging fact that some people who are infected with the Omicron variant suffer little more than a cough and runny nose — if they show symptoms at all.

While some places have maintained limits like restrictions on indoor dining for the unvaccinated, there is little appetite for broad shutdowns. A restaurateur in Austin, Texas, said that customers were out and about, eager to gather in groups.

“It’s obvious: People are over it,” said Daniel Brooks, 45, who owns two restaurants in Austin.

For the most part, American life has not locked down in the latest wave — businesses remain open and schools are largely in session in person — yet this variant has brought significant disruptions to daily life and threatens to bring still more.

Police officers, paramedics and firefighters have been sidelined with the virus, affecting response times in some cities. Across the country, millions of Americans have been sick at home in recent days, igniting debates over testing and safety measures in schools and alarming officials who told the public in blunt terms this past week that they were running dangerously low on hospital beds and health care workers.

“I suspect just about everybody in the state now either has just had Covid, has it today or knows somebody who does,” Gov. John Bel Edwards of Louisiana said. “There has never been more of the disease in our state.”

Omicron emerged in southern Africa in late November, and by Christmas it was the dominant variant in the United States, Britain and parts of continental Europe, including Denmark and Portugal, which have some of the highest vaccination rates in the world.

The record-high caseloads fueled by Omicron have produced their own form of chaos globally, sidelining millions of workers with infections, prompting shortages of test kits and forcing many governments to reimpose social restrictions. Spain, Greece and Italy ordered their citizens to return to wearing masks outdoors; the Netherlands retreated into full lockdown.

The variant is now battering nearly every corner of the world. India, bracing for a tidal wave of infections with only half its population vaccinated, has set up makeshift Covid wards in convention halls. In Argentina recently, the test positivity rate rose to a staggering 30 percent.

But with signs that the wave of Omicron in South Africa is receding, without bringing a huge new surge of deaths, many countries have moved to a strategy of living with the virus, opting to keep businesses and schools open rather than risk the economic havoc of more lockdowns.

Health officials in the United States, weary from two years of repeating similar pleas to the public, have tried to emphasize that the Omicron variant is like no other phase of the pandemic.

Daily case reports have roughly quintupled over the last month as Omicron has taken hold. About 650,000 new cases are being identified each day, more than twice as many as at last winter’s peak — a number that is certainly an undercount, since it does not include many results from at-home antigen tests.

So far, hospitalizations have increased at a much slower pace than cases. But the number of coronavirus patients is still growing rapidly, to about 134,000 nationwide, up from about 67,000 a month ago. In many cities, doctors say, a smaller proportion of Covid patients are landing in intensive care units or requiring mechanical ventilation, but the sheer number of patients is raising alarms.

Deaths, which are a lagging indicator, have not yet increased as significantly. About 1,500 deaths from Covid-19 are being announced every day in the United States. It could be weeks, officials said, before they will know whether the Omicron variant will result in another large wave of deaths in the United States, where more than 830,000 people have died from the coronavirus.

Andrew Noymer, a public health professor at the University of California, Irvine, said that the Omicron variant has been “legitimately complicated” for many Americans to comprehend, since it clearly differs from previous variants.

“Omicron is milder than Delta, but it’s more transmissible,” he said. “It’s changing two things at once.”

Shifting advice on isolation and quarantines from the Centers for Disease Control and Prevention has also left Americans with questions about the seriousness of the variant. Many employers, acting on guidance from public health officials, have encouraged sick workers to return to their jobs after only five days, even without a test showing that they are negative for the virus.

“The confusion is compounded,” said Dr. Gill Wright, the city health director in Nashville. “People are saying, this is supposed to get really bad, but we can go back to work quicker?”

In rural Michigan, people with coronavirus symptoms have arrived at hospitals in recent weeks repeating the conventional wisdom that once you have had Covid, you are unlikely to contract it again quickly.

“A lot of them say, ‘It can’t be Covid, I just had it a few months ago,” said Dr. Mark Hamed, an emergency room physician in Sandusky, Mich. “Lo and behold, they test positive.”

Roughly 62 percent of Americans are fully vaccinated, a number that has barely budged in recent weeks. Even fully vaccinated and boosted individuals have become infected with the Omicron variant, though health officials say that their infections appear less severe than in the unvaccinated.

Across the country, record numbers of public employees have been off the job as a result of surging coronavirus infections, leaving officials scrambling to reassure residents that if they call 911, someone will show up — if a little later than normal.

In Dallas, 204 of the roughly 2,100 employees of the city’s fire and rescue department were in quarantine on Thursday because of positive Covid-19 tests — the most since the beginning of the pandemic, according to Jason Evans, the department’s spokesman. He said that approximately one-quarter of the department’s total positive tests since March 2020 were from the last two weeks.

Los Angeles city officials said at a news conference on Thursday that almost 300 firefighters were off duty because of the virus, the most the department had seen at any one time. Jeff Cretan, a spokesman for Mayor London Breed of San Francisco, said that 140 employees of the fire department and 188 employees of the city police department had tested positive or were out because of quarantine protocols; so were 110 workers at the city’s transit agency.

Schools and colleges were facing the uncertainty of whether to conduct classes in person or virtually, sometimes while balancing competing arguments from parents, teachers and students.

In Chicago last week, the powerful teachers union and Mayor Lori Lightfoot clashed over coronavirus safety and testing in a dispute that has closed schools for several days in the nation’s third-largest school district.

At Rhodes College, a small liberal arts school in Memphis, officials announced over the holiday break that the start of in-person classes was being delayed two weeks — a disappointment for students exasperated with online classes and eager for the kind of college experience they had hoped for.

“Every semester, it feels like we’re almost back to normal and then it gets revoked one more time,” said John Howell, a senior political economy and philosophy major starting his final semester. “It feels like every routine is going to be broken and you should just expect that.”

Bishop James Dixon, the senior pastor at the Community of Faith Church in Houston, said that he and his fellow church leaders have found themselves struggling to strike the right balance as Omicron spreads.

“No one has a set answer,” he said. “It’s trial and error. It’s trepidatious. And we’re supposed to be people of faith and make a decision and take a direction.”

Mr. Dixon said the virus had caused a scare among many congregants because they know so many people now who have gotten it.

“Things are better than they were,” he said, “but simultaneously they’re worse than they were because numbers are soaring.”

Shashank Bengali contributed reporting from London, Jill Cowan from Los Angeles, J. David Goodman from Houston, Rick Rojas from Nashville and Mitch Smith from Chicago.