Once again, the coronavirus is ascendant. As infections mount across the country, it is dawning on Americans that the epidemic is now unstoppable, and that no corner of the nation will be left untouched.

Researchers have long known that masks can prevent people from spreading airway germs to others — findings that have driven much of the conversation around these crucial accessories during the coronavirus pandemic.

 The number of people infected with the coronavirus in different parts of the United States was anywhere from two to 13 times higher than the reported rates for those regions, according to data released Tuesday by the Centers for Disease Control and Prevention.

The findings suggest that large numbers of people who did not have symptoms or did not seek medical care may have kept the virus circulating in their communities. The study is the largest of its kind to date, although some early data was released last month.

“These data continue to show that the number of people who have been infected with the virus that causes Covid-19 far exceeds the number of reported cases,” Dr. Fiona Havers, the C.D.C. researcher who led the study, said in an email. “Many of these people likely had no symptoms or mild illness and may have had no idea that they were infected.”