Covid-19 infections in the United States may have been four times greater than the number of reported cases, with 1 in 7 US residents infected in mid-November, according to a new study.
On November 15, about 10.8 million reported cases of Covid-19 were reported to the United States Centers for Disease Control and Prevention, but the study suggests that the actual number of infections was close to 46.9 million.
The study also suggests that approximately 35% of Covid-19 deaths cannot be reported.
“The reported cases of Covid-19 do not represent the total burden of SARS-CoV-2 disease,” wrote the researchers in the study, published in the medical journal JAMA Network Open on Tuesday.
The researchers tested blood samples selected at random for the presence of Covid-19 antibodies in a series of surveys conducted in 10 states, plus one across the country. They derived estimates for the number of infections, hospitalizations and deaths in the United States as of November 15, comparing the prevalence of antibodies in the samples with the number of cases reported to adjust for underreporting.
The gaps between the number of reported infections and the estimated number of infections have narrowed over time, suggesting broader access to tests in later months, according to the researchers.
The data in this study can be useful in monitoring progress towards collective immunity as infections continue to increase, but there is still a long way to go.
“Even after adjusting for underreporting, there remains a substantial gap between the estimated proportion of the infected population and the proportion of infected people needed to achieve collective immunity,” wrote the researchers.