Covid-19 infections in the US were potentially four times higher than the number of reported cases, according to a new study. Every seventh US citizen was infected by mid-November.
As of November 15, approximately 10.8 million reported cases of Covid-19 had been reported to the U.S. Centers for Disease Control and Prevention. However, the study suggests that the actual number of infections was closer to 46.9 million.
The study also suggests that around 35% of Covid-19 deaths may go unreported.
“Reported Covid-19 cases do not represent the full exposure to SARS-CoV-2,” wrote the researchers in the study, which was published Tuesday in the medical journal JAMA Network Open.
The researchers tested random blood samples for the presence of Covid-19 antibodies in a series of surveys conducted in 10 states as well as one nationwide. They derived estimates for the number of infections, hospitalizations, and deaths in the U.S. as of November 15 by comparing the antibody prevalence in the samples with the number of reported cases to make up for underreporting.
The gaps between the number of reported infections and the estimated number of infections decreased over time, suggesting wider access to testing in later months, according to the researchers.
Data from this study can be helpful in monitoring progress toward herd immunity as infections continue to rise, but there is still a long way to go.
“Even after adjusting for underreporting, there remains a significant gap between the estimated percentage of the infected population and the percentage of infected people required to achieve herd immunity,” the researchers wrote.