Results of California Representative Sample Antibody Test Are In

Raleigh, N.C. — Earlier today, results of a California representative sample antibody test were released. Below are excerpts from the study, led in part by Stanford University School of Medicine and University of Southern California School of Public Policy.

Senate Leader Phil Berger (R-Rockingham) said, “These are results from one study in one county, but it is encouraging. We’re finally getting a better idea of the nature of this virus and how prevalent it is. I’m excited that a similar effort is underway through Wake Forest Baptist Health and Atrium Health, with collaboration from Stanford University researchers. Hopefully, we can soon obtain more reliable data to inform major public policy decisions.”

Excerpts from the study

· To date, in the absence of seroprevalence surveys, estimates of the fatality rate have relied on the number of confirmed cases multiplied by an estimated factor representing unknown or asymptomatic cases to arrive at the number of infections. However, the magnitude of that factor is highly uncertain.

· On April 3rd and 4th, 2020 we conducted a survey of residents of Santa Clara County to measure the seroprevalence of antibodies to SARS-CoV-2 and better approximate the number of infections. Our goal is to provide new and well-measured data for informing epidemic models, projections, and public policy decisions.

· Our data imply that, by April 1 (three days prior to the end of our survey) between 48,000 and 81,000 people had been infected in Santa Clara County. The reported number of confirmed positive cases in the county on April 1 was 956, 50–85-fold lower than the number of infections predicted by this study.

· The under-ascertainment of infections is central for better estimation of the fatality rate from COVID-19.

· If our estimates of 48,000–81,000 infections represent the cumulative total on April 1, and we project deaths to April 22 (a 3 week lag from time of infection to death), we estimate about 100 deaths in the county. A hundred deaths out of 48,000–81,000 infections corresponds to an infection fatality rate of 0.12–0.2%.

· Our prevalence estimates can be used to update existing fatality rates given the large upwards revision of under-ascertainment.

· [Our study] suggests that the number of infections is 50–85-fold larger than the number of cases currently detected in Santa Clara County. These new data should allow for better modeling of this pandemic and its progression under various scenarios of non-pharmaceutical interventions.

· These results represent the first large-scale community-based prevalence study in a major US county completed during a rapidly changing pandemic, and with newly available test kits. We consider our estimate to represent the best available current evidence, but recognize that new information, especially about the test kit performance, could result in updated estimates.

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