Seroprevalence of SARS-CoV-2–Specific Antibodies Among Adults in Los Angeles County, California, on April 10-11, 2020

On January 30, 2020, the World Health Organization (WHO) declared SARS-CoV-2 a global pandemic, based on a high infection rate and a high case fatality rate (CFR). The combination of these two points led WHO to forecast a high expected mortality rate of approximately 2% of the population. The phenomenon of Simpson's paradox teaches us that we should be careful when we combine two variables together. Indeed, despite the high mortality rate in several places, this forecast seems to have collapsed. We believe one of the reasons for the erroneous forecasts is that combining the above points ignored a confounding variable - many of the virus carriers are asymptomatic and therefore not diagnosed.