Harsh measures, including stay-at-home orders and restaurant closures, are contributing to rapid drops in the numbers of fevers — a signal symptom of most coronavirus infections — recorded in states across the country, according to intriguing new data produced by a medical technology firm.

At least 248 million Americans in at least 29 states have been told to stay at home. It had seemed nearly impossible for public health officials to know how effective this measure and others have been in slowing the coronavirus.

But the new data offer evidence, in real time, that tight social-distancing restrictions may be working, potentially reducing hospital overcrowding and lowering death rates, experts said.

The company, Kinsa Health, which produces internet-connected thermometers, first created a national map of fever levels on March 22 and was able to spot the trend within a day. Since then, data from the health departments of New York State and Washington State have buttressed the finding, making it clear that social distancing is saving lives.