CHICAGO — 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 past 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 would 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.”A bar in the River North neighborhood of Chicago last week. Most Americans are meeting a new Covid wave with a collective shrug.Jamie Kelter Davis for The New York TimesComplicating 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.Coronavirus cases in the United States by regionThis chart shows how reported cases per capita have changed in different parts of the country.