The death toll from COVID-19 in the United States could exceed 500,000 by February unless nearly all Americans wear face masks, researchers said on Friday, as the country set a new single-day record for new cases.

The latest estimate by the widely cited University of Washington’s Institute for Health Metrics and Evaluation (IHME) reflects concern that cold winter weather will drive Americans indoors, where the coronavirus spreads more easily, particularly in confined, poorly-ventilated spaces.

Some 84,218 people were diagnosed with COVID-19 across the United States on Friday, according to a Reuters tally, breaking the single-day record of 77,299 that was set on July 16. Only India has reported more cases in a single day: 97,894, on September 17.

“We are heading into a very substantial fall/winter surge,” said IHME director Chris Murray, who co-led the research.

The number of possible deaths could drop by 130,000 if 95 percent of Americans covered their faces, the IHME said, echoing a recommendation by Dr Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

The country’s Health Secretary Alex Azar has attributed the increase in cases nationwide to individual behaviour, saying household gatherings have become a “major vector of disease spread.”

Asked about President Donald Trump’s claim that the US was “rounding the turn” on the pandemic during Thursday night’s presidential debate, Azar told CNN that Trump was trying to provide hope to Americans waiting for a vaccine.

Pennsylvania, a swing state that is expected to play a crucial role in the November 3 presidential election, reported its largest single-day increase in cases since the pandemic began. “Daily increases are now comparable with what we saw in April 2020,” the Pennsylvania Department of Health said in a statement issued on Friday.

Also reporting record one-day increases were the states of Alaska, Arkansas, Illinois, North Carolina, North Dakota, Ohio, Oregon, Rhode Island, South Dakota, Tennessee, Utah, Wisconsin and Wyoming.

More in hospital

On Thursday, there were 916 reported fatalities in the US, a day after the country recorded over 1,200 new deaths for the first time since August.

Also on Thursday, the number of COVID-19 patients in US hospitals climbed to a two-month high. There are now more than 41,000 people in hospital with coronavirus across the country, up 34 percent since the start of the month, according to a Reuters analysis.

North Dakota, with 887 new cases on both Thursday and Friday, remains the hardest-hit state, based on new cases per capita, followed by South Dakota, Montana and Wisconsin.

Eight states reported record numbers of COVID-19 patients in hospital on Friday: Alaska, Kentucky, New Mexico, North Dakota, Ohio, Oklahoma, West Virginia and Wyoming.

Chicago Mayor Lori E Lightfoot announced a curfew on non-essential businesses beginning at 10pm on Friday (03:00 GMT on Saturday). She warned residents to avoid social gatherings of more than six people and end all gatherings by 10pm.

Nearly 2,500 people are in hospital with COVID-19 in Illinois, the state’s top public health official, Dr Ngozi Ezike, told a news conference.

The Northeast remains the one region of the county without a significant surge in cases, but infections are trending higher. Boston public schools shifted to online-only learning this week.