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An estimated 16.8 million U.S. adults had undiagnosed COVID-19 by July 2020, representing 4.6% of U.S. adults and 4.8 undiagnosed infections for every diagnosed case, according to a  published yesterday by the journal Science Translational Medicine. NIH’s SARS-CoV-2 Seroprevalence Project used an enzyme-linked immunosorbent assay to identify SARS-CoV-2 antibodies in dried blood samples collected from a representative sample of U.S. adults.

Black study participants had the highest rate of undiagnosed infection (14.2%), followed by Native American/Alaska Native (6.8%), Hispanic (6.1%), white (2.5%) and Asian (2%) participants. Adults under 45 had the highest rate by age (5.9%); women had a higher rate (5.5%) than men (3.5%); and urban residents a higher rate (5.3%) than rural residents (1.1%). The Mid-Atlantic (8.6%) and Northeast (7.5%) had the highest rates by region and the Midwest the lowest (1.6%). 

“This study helps account for how quickly the virus spread to all corners of the country and the globe,”  Bruce Tromberg, director of the National Institute of Biomedical Imaging and Bioengineering. “The information will be invaluable as we assess the best public health measures needed to keep people safe, as new—and even more transmissible—variants emerge and vaccine antibody response changes over time.”