A rapidly rising flood of coronavirus infections engulfed much of the United States on Thursday, setting records for new cases in 20 states, killing 1,158 people and straining the health system’s capacity to keep up with the pandemic.

On Thursday, 116,707 new cases were reported, the second straight record for a single day and a figure that dwarfed the total for any day in the previous worst two periods of the outbreak, in April and July. From Washington state to West Virginia and from Texas to Pennsylvania, the country was awash in record or near-record case counts Thursday.

Illinois reported 9,935 new cases, Iowa registered 4,562 and Oklahoma recorded 2,094 — all single-day highs — as the virus continued to spread across the nation’s midsection and the Plains states.

“In many areas of the country, this pandemic is a runaway train,” said James Lawler, an infectious-diseases specialist at the University of Nebraska Medical Center. “We are doubling covid hospitalizations every two to three weeks in many parts of the Midwest. Think about what that means in a month to six weeks. So, we better find the brakes soon.”

In a nation deeply fractured over whether to reopen the economy or confront the pandemic with tough restrictions, the virus has flourished, experts said, taking advantage of cooler winter months, lower humidity and communities where mitigation measures are less strict or are not being followed.

“The division is itself the big hurdle,” said Tom Frieden, director of the Centers for Disease Control and Prevention during the Obama administration. “If we look around the world, the places that have struggled most in controlling the virus are those with the least social cohesion. Fighting the virus requires the notion that we’re all in this together.”

Case counts tend to be higher midweek, a result of the reporting patterns from hospitals and health departments. As of Thursday, the virus had killed more than 234,000 people and infected more than 9.5 million, according to data analyzed by The Washington Post. On Wednesday, the United States recorded more than 100,000 new cases in a single day for the first time since the pandemic reached the country in January.

That number was quickly surpassed Thursday.

In El Paso, University Medical Center has set record highs the past three days for inpatients with covid-19, the disease caused by the virus, said Ryan Mielke, director of public affairs.

“At the end of October, we were right around 30 inpatients,” Mielke said. “Yesterday, we had 225. In October, we had one floor dedicated to covid-19 patients. Now, we have multiple floors, wholly dedicated to covid-19 patients.”

The hospital, the city’s largest, has moved some patients with other illnesses to El Paso Children’s Hospital to free up beds for covid-19 patients. The city’s convention center has been outfitted to accept patients. The state of Texas has deployed more than 130 nurses, doctors, respiratory therapists and other workers to University Medical Center to help in the crisis, Mielke said.

David Wyatt, an intensive-care nurse at University Medical Center who had just finished a 14-hour shift Wednesday, said his hospital is feeling the strain.

“The hospitals are just getting overrun,” he said.

Lawler’s medical facility in Omaha is “setting records every day,” he said. “We are seeing more and more cases, and our hospitals are filling up rapidly. Welcome to the concept of exponential growth.”

Nationally, the mortality rate from covid-19 has declined, in part because doctors have learned to use medications such as the steroid dexamethasone and techniques such as proning — laying patients on their stomachs to ease their ability to breathe. But increases in deaths lag behind rises in the case count by several weeks. Authorities expect that to occur again in November and December, and mortality rates could rise if hospitals are overwhelmed.

“If your ventilators are being run by a dermatologist, your outcomes are not going to be good,” Lawler said.

Janis M. Orlowski, chief health-care officer for the Association of American Medical Colleges, said “in those areas where there’s an explosion, like Utah, like Nebraska, like in the Dakotas, like Colorado, we are seeing what we saw in the South at the end of the spring and the beginning of the summer. . . . The hospitals are overrun. There are no ICU beds.”

Health-care workers are taking off work because they are sick, burned out or have child-care problems, she said.

“Are we smarter from understanding the disease from six months ago? Yes,” she said. “Do we have our hands around having adequate supplies? No.”

Michael Fraser, chief executive of the Association of State and Territorial Health Officials, which represents state health departments, said the election has also played a role in the public health response.

“There’s been this sense of people giving up,” he said. “You had state leaders looking at the election and deciding it was not worth taking bold, unpopular moves against the virus that might save lives but hurt your side politically. There’s been state health officials debating whether to continue telling people to do things, because they know many are not going to listen.”

With the election over, “we as health officials have got to get back to the work,” he added. “This thing has been allowed to run its course unchecked.”

One bright spot is the effort to develop vaccines and therapeutics, which continues to plow ahead at a record pace, though neither will be widely available soon enough to blunt the surge of cases this winter.

Two companies, Eli Lilly & Co. and Regeneron Pharmaceuticals, have developed laboratory-brewed antibody drugs that show promise in protecting recently infected people from developing severe disease. President Trump received one of the drugs under a compassionate-use provision to treat his case of covid-19 and declared it a “cure” that he would make freely available.

Both companies have applied for emergency authorization from regulators to provide those drugs, but even if the companies receive clearance imminently, the supply will be limited.

The drugmakers collectively project they will have 1.3 million doses manufactured by early next year. The U.S. government has secured 600,000 of those. Those factors will make it essential to limit use of the drugs to people at highest risk for severe disease.

But they have so far had disappointing results in trials of the sickest hospitalized patients.

The race for a vaccine is breaking every scientific speed record, but a vaccine will not be ready to quell the current outbreak even under the most optimistic timeline.

Two leading companies, Pfizer and Moderna, have projected they could have enough data to apply for regulatory clearance for their vaccine candidates as early as late November.

If a vaccine is shown to be effective, scaled-up production should mean that the highest-risk people, such as health-care workers, could receive injections right away, instead of waiting months or years for factories to come online.

Leaders of Operation Warp Speed, the federal effort to hasten vaccine and therapeutic development, have projected having 600 million to 700 million doses of vaccine by March or April. But that does not mean all those doses will be proved safe and effective, and turning vaccines into vaccinations for the entire population is a gargantuan project that could take months.

In the meantime, public health authorities continue to urge simple mitigation measures that have proved effective throughout the pandemic: wearing masks; maintaining distance from other people; avoiding large gatherings, especially indoors; and washing hands frequently.

“People think there’s some magical ceiling we’re going to hit. There is no ceiling,” Lawler said. “Not until we hit herd immunity. And that’s not going to be a pretty picture.

“It’s possible to control it. People have to listen to actual public health authorities and not their friend on Facebook.”

Hinojosa reported from El Paso. Jacqueline Dupree and William Wan in Washington contributed to this report.