A new study released by the National Institutes of Health reports that the prevalence of COVID-19 in the United States during spring and summer of 2020 far exceeded the known number of cases. The study reported that for every diagnosed COVID-19 case in this time frame, the researchers estimate that there were 4.8 undiagnosed cases, representing an additional 16.8 million cases by July alone!
“This study helps account for how quickly the virus spread to all corners of the country and the globe,” said Bruce Tromberg, Ph.D., director of the National Institute of Biomedical Imaging and Bioengineering (NIBIB), one of the NIH institutes who run the NIH SARS-CoV-2 Seroprevalence Project. “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.”
“A hallmark of the coronavirus pandemic is that there are people infected with the virus that causes COVID-19 who have few or no symptoms,” said Matthew J. Memoli, M.D., M.S., director, Clinical Studies Unit, Laboratory of Infectious Diseases, NIAID. COVID-19 illness can range from short-lived cough, fatigue and fever to severe illness that could lead to hospitalization and death. Asymptomatic SARS-CoV-2 infection, which is rarely diagnosed, is a silent source of viral spread. While not causing overt signs of illness, undiagnosed infection poses a danger to the public and is a critical factor necessitating public health resources and strategies for addressing the pandemic.
The team observed that:
- each diagnosed case of COVID-19 corresponds to an estimated 4.8 undiagnosed cases of the disease during this time frame,
- the youngest participants—those between the ages of 18 and 44—had the highest estimated seropositivity, at 5.9%,
- estimated seropositivity was higher in females than in males (5.5% versus 3.5%, respectively),
- participants in the Mid-Atlantic and Northeast regions had the highest rates (8.6% and 7.5%, respectively), and participants in the Midwest had the lowest rates (1.6%),
- urban participants had a higher estimated seropositivity (5.3%) compared with rural participants (1.1%), and
- Black/African American respondents had the highest estimated seropositivity rate (14.2%), followed by Native American/Alaska Native (6.8%), Hispanic (6.1%), white/Caucasian (2.5%), and Asian (2%) respondents.
“The estimate of COVID-19 cases in the United States in mid-July 2020, 3 million in a population of 330 million, should be revised upwards by almost 20 million when the percent of asymptomatic positive results is included,” said senior co-author Kaitlyn Sadtler, Ph.D., chief of the NIBIB Section on Immunoengineering. “This wide gap between the known cases at the time and these asymptomatic infections has implications not only for retrospectively understanding this pandemic, but future pandemic preparedness.”
The researchers are currently following up with the enrolled participants to evaluate the six- and 12-month status of seroprevalence; it will include new analyses to differentiate antibodies from infection versus antibodies from vaccination, as well as antibody reactivity to variants of concern.
Source: National Institutes of Health
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