OREANDA-NEWS Covid-19 is surging around the United States again in what experts consider the most transmissible variant of the pandemic yet.

But something is different this time: The public health authorities are holding back.

In Chicago, where the county’s Covid warning level was raised to “high” last week, the city’s top doctor said there was no reason for residents to let the virus control their lives. The state health director in Louisiana likened a new rise in Covid cases there to a downpour — “a surge within a surge” — but characterized the situation as concerning but not alarming.

And the public health officer in King County, Wash., Dr. Jeffrey Duchin, said on Thursday that officials were discussing reissuing a mask mandate but would prefer that the public mask up voluntarily. “We’re not going to be able to have infinite series of mandates forcing people to do this, that and the other,” he said.

The latest surge, driven by a spike of BA.5 subvariant cases in this country since May, has sent infections rising in at least 40 states, particularly in the Great Plains, West and South. Hospitalizations have climbed by 20 percent in the last two weeks, leaving more than 40,000 people in American hospitals with the coronavirus on an average day.

More than two years after the pandemic began, though, public health officials are sounding only quiet warnings amid a picture that they hope has been changed by vaccines, treatments and rising immunity. Deaths are rising, but only modestly so far in this new wave. And state and local public health officials say they also must now factor in a reality that is obvious along the streets from Seattle to New York City: Most Americans are meeting a new Covid wave with a collective shrug, shunning masks, joining crowds indoors and moving on from the endless barrage of virus warnings of months past.

“I feel strongly that you can’t just kind of cry wolf all the time,” said Dr. Allison Arwady, the commissioner of the Chicago health department, who said she will wait to see whether hospitals become strained before considering another citywide mask mandate. “I want to save the requirements around masks or updating vaccine requirements for when there’s a significant change.”

Complicating the country’s understanding of this BA.5 wave is a dearth of data. Not since the earliest months of the pandemic has there been so little precise information about the number of actual infections in the United States. As public testing sites have closed and at-home testing — if people test at all — has grown common, the publicly reported data has become scarce and spotty.

Still, experts say, the outlines of a new wave are undeniable.

“You don’t have to count every raindrop to know it’s raining,” said Dr. Joseph Kanter, Louisiana’s state health officer and medical director. “And it’s pouring right now.”

In that state, the health department analyzes a wide range of data to track the spread of the virus, including case counts, samples from a growing network of wastewater testing sites, test positivity rate and hospitalization metrics.

The BA.5 subvariant, which was first detected in South Africa in January and spread to a number of European countries, was responsible for 1 percent of cases in the United States in mid-May but now represents at least two-thirds of new cases in the country.

Anita Kurian, an assistant director for the health department in San Antonio, said cases have been rising in the area for six weeks in a row. But some measures, like the low number of deaths so far, suggest that the nation is entering a newer and less lethal stage of the pandemic where vaccines and treatments have significantly improved chances of survival, she said.

“We are nowhere at the level where we were with the previous surges,” she said.

So far, the current wave’s toll of hospitalizations and deaths pales in comparison to previous spikes. During the peak of the Omicron surge in early 2022, close to 159,000 people were hospitalized on any given day.

Experts caution that predicting the months ahead is difficult, particularly given the high transmissibility of BA.5. Words of caution from national health leaders have slowly increased in intensity in recent weeks.

Still, even as federal health authorities reiterated calls for people to test for Covid before attending large indoor gatherings or visiting especially vulnerable, immunocompromised people, they are striking a delicate balance, telling Americans that while they do not need to upend their lives, they must pay attention to the Covid threat.

“We should not let it disrupt our lives,” Dr. Anthony S. Fauci, Mr. Biden’s chief medical adviser on the virus, said at a White House news briefing in which he added that new variants could continue to emerge. “But we cannot deny that it is a reality that we need to deal with.”

As health officials in many places have avoided issuing new virus restrictions during the latest surge, California has stood out as an exception. There, public health authorities have issued stark warnings and moved toward reimposing restrictions.

The warnings have been spurred by worrisome data, experts said. Walgreens said that more than half of the Covid tests administered at its California stores have returned with positive results. Surveys of wastewater in the Bay Area suggest this surge could be the biggest yet.

And the number of weekly deaths in Los Angeles County from the coronavirus has doubled from around 50 a month ago to 100 last week. The deaths are still below the levels of the winter Omicron surge, when more than 400 were dying weekly in the county.

Officials in Los Angeles say they plan to reinstate a countywide indoor mask mandate as early as the end of this month. Barbara Ferrer, the public health director in the county, said that even a slight increase in masking would help slow transmission of the virus.

“I’m like everyone else: I hate wearing that mask. But more than that, I hate the idea that I might accidentally transmit to somebody else,” Ms. Ferrer said. “That’s my biggest fear — that we’re so anxious to be done with this virus that we’re getting complacent.”

Charles Chiu, an infectious disease specialist and virologist at the University of California, San Francisco, says data emerging from patients suggests that BA.5 does not cause more severe disease in patients than other Omicron variants. But he says he is concerned that the variant is so infectious and so able to evade the protections of vaccination and prior infection that it could be unstoppable.

“It looks as if we are unable to control it,” he said.

Dr. Chiu said he was sympathetic to the plight of government officials seeking to mitigate the spread of the virus. They are up against a public that chafes at renewed directives, even in parts of the country where people were previously most willing to go along. In places where Covid mitigation measures are mandatory, like on New York subways, adherence to masking rules is increasingly spotty.

“Public health officers have an impossible task here,” Dr. Chiu said.

In New York City, rates of positive tests, cases and hospitalizations are all rising. But health officials have resisted reissuing mask mandates, and many residents have said they were not worried, counting on vaccines, immunity from prior infections and antivirals for protection from severe illness. The city no longer has a contact tracing system in place or requires proof of vaccination to enter restaurants.

In Louisiana, officials have watched hospitalizations of people with Covid rise in the state, but they say those numbers are still far lower than in previous surges when more than 2,000 residents were at times hospitalized.

“I feel much more empowered that we have the ability to protect ourselves,” Dr. Kanter said.

During the height of the Delta wave in Louisiana in 2021, about 20 percent of hospitalized Covid patients were on ventilators, according to Dr. Kanter, the state health officer and medical director. That figure fell to 10 percent during the state’s initial Omicron surge and now is below 5 percent.

For people who are most at risk of severe illness from Covid, a sense that public health warnings have diminished was little comfort, and in fact, made them worry more than ever about getting infected.

Neyda Bonilla, 48, of Mission, Texas, was diagnosed in April with breast cancer. With case counts rising in South Texas, she now fears that an infection as she undergoes chemotherapy could prove catastrophic for her health.

She has received all of the vaccines and boosters available to her, she said, and now wears a surgical mask in public and rarely leaves the house, except to work as an administrator at an ambulance company.

“I hope that people open their eyes,” she said. “We should have never taken our masks off. This is not over.”

Yet even in some cities whose residents have taken precautions against Covid throughout the pandemic, the latest surge has not caused widespread alarm.

In Berkeley, Calif., Jeff Shepler, the general manager of the Spanish Table, a specialty shop selling Iberian wine and food, said that he goes to Giants games across the Bay in San Francisco, recently attended a Pearl Jam concert at the Oakland Coliseum and does not hesitate to shake hands.

“It got exhausting for me to wear a mask all day, every day,” he said. “I’m at the point in my life where I’ve got the vaccine and I’ve had Covid. I figure I’m fairly safe.”

Julie Bosman reported from Chicago, Thomas Fuller from San Francisco, and Edgar Sandoval from San Antonio, Texas. Soumya Karlamangla, Eliza Fawcett, Sarah Cahalan , and Holly Secon contributed reporting.