Covid-19 infections in the United States may have been four times higher than the number of cases reported, with 1 in 7 US residents infected by mid-November, according to a new study.
As of November 15, about 10.8 million reported cases of Covid-19 were reported to the US Centers for Disease Control and Prevention, but the study suggests the actual number of infections was closer to 46.9 million.
The study also suggests that approximately 35% of Covid-19 deaths may not be reported.
“Reported Covid-19 cases do not represent the full SARS-CoV-2 disease burden,” the researchers wrote in the study, published in the medical journal JAMA Network Open on Tuesday.
Researchers tested randomly selected 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 US as of Nov. 15 by comparing antibody prevalence in the samples to the number of reported cases to adjust for underreporting.
Gaps between the number of reported infections and estimated number of infections decreased over time, suggesting more widespread access to testing in later months, according to the researchers.
Data from this study may 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, a substantial gap remains between the estimated proportion of the population infected and the proportion infected required to reach herd immunity,” the researchers wrote.