The coronavirus pandemic appears to be leveling off in most of the United States, with new cases, deaths and hospitalizations all down over the past week, but the plateau leaves the country with high and persistent infection numbers and worries of a ­post-Labor Day surge in some areas.

The number of new cases reported daily peaked above 70,000 in July and has been falling since. The decline now seems to be slowing, with the daily number hovering near 40,000 for more than a week, a review of nationwide data showed Tuesday. That is one sign that the infection may be leveling off.

Although that is good news, the numbers suggest continued high levels of infection and a long road ahead, particularly as cold weather and the flu season approach. Without a vaccine or a major advance in treatment, significant reductions in new cases would probably require voluntary or mandated changes in behavior that experts say are unlikely six months into the public health crisis.

Although the pandemic has meant the loss of jobs, wages, schooling and more along with lost lives, large numbers of Americans have resumed many elements of their daily routines, and many still decline to wear masks or avoid crowds.

Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, said he no longer thinks it makes sense to talk about “waves” of virus spread. Instead, he said, there will be spikes followed by plateaus.

“This is just one big forest fire of coronavirus, and it will burn hot wherever there is human wood to burn,” he said. “If you don’t put the fire out completely, and then you walk away from it, it’s going to start burning again in days.”

But instead of remaining vigilant, he said, a growing number of Midwesterners have begun to doubt the existence or severity of the virus. Cases in Minnesota traced to weddings and funerals are on the rise.

“We have a very short-term memory as a population, in terms of what can happen in our communities,” he said.

Anthony S. Fauci, the chief expert for infectious disease at the National Institutes of Health, warned in an interview that eight states were at risk of new spikes in cases: North Dakota, South Dakota, Montana, Iowa, Arkansas, Missouri, Indiana and Illinois.

“It’s almost like whack-a-mole,” Fauci said of the rise in cases in the Midwest as cases in the South decline. “It’s quite frustrating . . . we never really get down to a very, very low baseline.”

Although the full picture from the Labor Day weekend will take some days to emerge, cases spiked after the Memorial Day and July 4 holidays.

Minnesota reported more than 1,000 new cases in a single day for the first time on Aug. 27; it’s since crossed that benchmark two more times. Daily cases in Iowa have begun to creep into the thousands as well. In North and South Dakota, caseloads have tripled since July 4.

Some governors have defended their hands-off approach to the virus even as caseloads climb. In South Dakota, Gov. Kristi L. Noem (R) went to the state fair over Labor Day weekend.

“You’ve heard me say many times that South Dakota never closed,” she wrote on Facebook. “. . . If business owners are sick and tired of the lockdowns in other states, I want them to know that they have another option. They can come to South Dakota.”

Iowa Gov. Kim Reynolds (R) did shut down bars in six counties where caseloads were rising, saying it was a last resort after many refused to comply with social distancing measures. But she has resisted broader crackdowns.

“I am trying to balance the health and safety of Iowans with the livelihood of these small businesses,” she said at a news conference Thursday.

In both Iowa and South Dakota, the percentage of tests coming back positive is in the double digits and trending upward. But the increases have yet to be reflected in hospitalizations and deaths, which are still higher in the Sun Belt and the Deep South.

Across the United States over the past week, new daily reported cases fell 6.7 percent while daily reported deaths from covid-19, the disease caused by the novel coronavirus, fell 9.3 percent. Covid-related hospitalizations fell 8.3 percent.

Among reported tests, the positivity rate was an average of 5.4 percent across the country. Centers for Disease Control and Prevention Director Robert Redfield had said last month that areas of the country with positive test rates above 5 percent should use remote teaching rather than in-person schooling.

Cases appear to have plateaued, but at twice the rate seen after Memorial Day weekend. Experts say what appears to be a lull is a combination of declining cases in the Sun Belt and alarming climbs in the Midwest.

From Memorial Day weekend through the unofficial end of the season Monday, the number of Americans who died of covid-19 shot up from just under 100,000 to more than 186,000, according to data tracked by The Washington Post, as infections nearly quadrupled to upward of 6.2 million.

As happened in the Sun Belt, people in their 20s and 30s are driving the surge in the Midwest; hospitalizations and deaths have yet to rise precipitously. In the South it took several weeks for those younger and healthier people to begin infecting an older and more vulnerable population.

Joshua Wynne, dean of the School of Medicine and Health Sciences at the University of North Dakota, says that doesn’t have to happen again.

“The history of other places makes us quite concerned,” he said, but “I do not think it’s a foregone conclusion that simply because we’ve seen an uptick in cases it’s going to necessarily lead to a dire outcome.” The key is whether, along with tamping down the spread among young people, officials can identify and quarantine them in time.

North Dakota had been spared a large outbreak for months. That made it an attractive destination for vacationers, Wynne said, who may have brought the virus with them. Then college students returned to campuses — as well as parties and bars — and began fueling the rise. The state went from a few dozen cases a day in July to more than 350 on Friday.

“Probably some of my fellow citizens let their guard down a bit since we had been doing so well for so long,” Wynne said. “We got a little lulled into a false sense of security.”

An economic analysis published this week by a German nonprofit used cellphone data to estimate that a motorcycle rally that brought nearly half a million people to Sturgis, S.D., last month led to 266,796 new cases across the country.

Health officials in South Dakota questioned that analysis in a news conference with reporters Tuesday. While “the risk of covid-19 does increase with the size of the gathering,” state epidemiologist Joshua Clayton said, the analysis “did not account for an already increasing case load” from reopening schools. The state has traced only 124 cases directly to attendance at the rally.

But that number does not include people who were infected by someone who went to Sturgis. Osterholm said that while only 53 cases in Minnesota are directly associated with the rally, for example, one attendee is believed to have infected an additional 72 people at a wedding.

It’s hard to trace and isolate rallygoers, he said, because they tend to be hostile to public health interventions: “We have numerous examples of people who went to Sturgis who are high risk and refuse to be tested.”

In the city of Sturgis alone, free tests were offered to 1,300 residents; only 650 people took advantage of them.

Meanwhile, the chief executives of nine drug companies pledged Tuesday not to seek regulatory approval before the safety and efficacy of their experimental coronavirus vaccines have been established in Phase 3 clinical trials. It was an extraordinary effort to bolster public faith in an eventual vaccine in the face of President Trump’s push to introduce one before Election Day.

“We believe this pledge will help ensure public confidence in the rigorous scientific and regulatory process by which covid-19 vaccines are evaluated and may ultimately be approved,” the executives wrote in a joint statement. The Wall Street Journal first reported Friday that a statement from the companies was forthcoming.

Trump’s desire to deliver a vaccine — or at least convince the public that one is very near — by Election Day is in part a campaign gambit to improve his standing with an electorate that overwhelmingly disapproves of his management of the pandemic.

Also Tuesday, Senate Majority Leader Mitch McConnell (R-Ky.) announced plans to vote on a slimmed-down coronavirus relief bill this week.

The legislation is not expected to advance, since that would require support from Democrats, who’ve held out for a larger package. McConnell has struggled even to unite Republicans behind the bill and is likely to suffer some GOP defections.

But a month after bipartisan talks collapsed on Capitol Hill, McConnell is aiming to put pressure on House Speaker Nancy Pelosi (D-Calif.) and Senate Minority Leader Charles E. Schumer (D-N.Y.) by unveiling legislation that would fund some key priorities, including small businesses, enhanced unemployment insurance, child care, the Postal Service and schools.

Global economic output could decline by 1.5 percent over the rest of the century because of disruptions to schooling caused by the pandemic, according to a new estimate from the Organization for Economic Cooperation and Development.

In the United States, that might mean a total economic loss equivalent to $15.3 trillion, the OECD estimated in a report released Tuesday. And it could get worse if the school disruptions end up going on for longer.

“These estimates assume that only the cohort currently in school are affected by the closures and that all subsequent cohorts resume normal schooling. If schools are slow to return to prior levels of performance, the growth losses will be proportionately higher,” the OECD said.

Brittany Shammas, Erica Werner and Adam Taylor contributed to this report.