JOIN USCovid-19 infections much higher than reported cases in parts of US, study shows
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 1 in 4 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 that 60% 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.
“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 CDC researcher who led the study.
About 40% 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.
The researchers analyzed blood samples from people who had routine clinical tests or were hospitalized to determine if they had antibodies against the coronavirus — evidence of prior infection. They had released early data from six cities and states in June. The study published in the journal JAMA on Tuesday expands that research by including four more regions.
The results indicate that in vast swaths of the country, the coronavirus still has touched only a small fraction of the population. In Utah, for example, just over 1% of people had been exposed to the virus by early June. The rate was 2.2% for Minneapolis-St. Paul as of the first week of June, 3.6% for the Philadelphia metropolitan region as of May 30 and 1% for the San Francisco Bay Area as of April 30.