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 indicates that even the hardest-hit area in the study — New York City, where nearly one in four people has been exposed to the virus — is nowhere near achieving herd immunity, the level of exposure at which the virus would stop spreading in a particular city or region. Experts believe 60 percent of people in an area would need to have been exposed to the coronavirus to reach herd immunity.
The analysis, based on antibody tests, is the largest of its kind to date; a study of a subset of cities and states was released last month.
“This is not coming as a shock or surprise to epidemiologists,” Carl Bergstrom, an infectious diseases expert at the University of Washington in Seattle, said in an email. “All along, we have expected that only about 10 percent of the cases will be reported.”
Tracking the numbers over time can provide useful insights into the virus’ spread and about a region’s capacity to cope with the epidemic, other experts said.