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.
“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,” said Dr. Fiona Havers, the C.D.C. researcher who led the study. “Many of these people likely had no symptoms or mild illness and may have had no idea that they were infected.”
About 40 percent of infected people do not develop symptoms, but they may still pass the virus on to others. The United States now tests roughly 700,000 people a day. The new results highlight the need for much more testing to detect infection levels and contain the viral spread in various parts of the country.
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For example, in Missouri, the prevalence of infections is 13 times the reported rate, suggesting that the state missed most people with the virus who may have contributed to its outsized outbreak.