WASHINGTON • Public health officials in the US could take heart at the end of the summer. Even as the coronavirus continued to spread, fewer people were winding up in the hospital because of Covid-19, and fewer were dying.

But now, as the seasons turn, there are signs suggesting there will be more deaths and serious illness ahead. Data collected by the Covid Tracking Project shows the number of people hospitalised has plateaued at about 30,000 in the past week, after a fall from nearly 60,000 that began in late July.

Deaths, meanwhile, averaged about 750 over the seven days through Sunday, higher than the roughly 600 deaths a day in the first week of July.

Scientists had hoped that a warm-weather reprieve could soften an expected re-emergence of the coronavirus in the colder months. Instead, the contagion continued to spread across the country after Memorial Day, with early summer outbreaks in Sun Belt states followed by the recent surge in the Upper Midwest and on college campuses nationwide.

History and science suggest the second winter with coronavirus is likely to be worse than the first.

"We haven't had exposure to Covid throughout an entire winter, when more people are indoors and close together for prolonged periods," said Dr William Schaffner, an infectious disease professor at Vanderbilt University in Nashville, Tennessee. "We are certainly concerned that Covid could spread even more readily in the winter than it has so far."

The Trump administration has pointed to the increasing availability of coronavirus tests as the reason the number of new cases in the United States remains high.

Increased testing has also made it possible to catch coronavirus cases earlier. That, combined with improved hospital care and medicines like Gilead Sciences' remdesivir and generic steroid dexamethasone, allowed more patients to survive their infections this summer.

However, a week-long plateau in new cases, hospitalisations and deaths are an early warning that things could be about to get worse.

Along with the resumption of school, more states are easing curbs on restaurants and bars, giving the virus more chances to find vulnerable people to infect.

States that had been doing well, including New York, are seeing a new surge. New York Governor Andrew Cuomo said there were 868 new cases on Sunday, an 18 per cent increase from two weeks earlier. Also, the percentage of Covid-19 tests taken in New York state that has come back positive has inched up to 1.5 per cent, Mr Cuomo said on Monday, a worrisome trend for the former epicentre of the country's coronavirus epidemic. New York's positivity rate had hovered around 1 per cent for weeks, a hard-won metric after the state tallied thousands of cases per day during the peak of its outbreak in the spring.

Country-wide, the number of new cases has risen for two weeks in a row in 27 out of 50 states, with North Carolina and New Mexico reporting increases above 50 per cent last week.

Separately, the US Centres for Disease Control and Prevention released detailed data on Monday that showed almost 280,000 children of school-going age were infected with the coronavirus between March 1 and Sept 19.

The figure accounted for roughly 4 per cent of the total US caseload over this period, with children aged 12-17 approximately twice as likely to be infected as those aged 5-11.

BLOOMBERG, REUTERS, AGENCE FRANCE-PRESSE