Early Antibody Studies in California Suggest High Infection Rates

But external experts say the data might be skewed

Researchers in California have released early data from two studies looking for antibodies against the novel coronavirus. The first study, which has not been peer-reviewed and was posted Friday on the preprint server medRxiv, showed that out of 3,300 people tested in Santa Clara County, 50 were positive for SARS-CoV-2 antibodies, a prevalence rate of 1.5%. However, the researchers increased the estimates for the county to between 2.49% and 4.16% after adjusting for demographics and test performance characteristics.

Using these estimates, the researchers project that between 48,000 and 81,000 people in the county have been infected with the novel coronavirus. This is 50- to 85-fold higher than the 956 confirmed cases the county reported at the time of the study. If correct, these numbers vastly lower the fatality rate from the virus to between 0.12% and 0.2%, down from the current projection of roughly 1%.

A second early look at antibody prevalence from Los Angeles County was released Monday in a press release from the Department of Public Health. The researchers — many of whom were also part of the Santa Clara study — estimate that between 2.8% and 5.6% of people Los Angeles County have antibodies to SARS-CoV-2, roughly translating to between 221,000 and 442,000 people. Again, these projections are 28 to 55 times higher than the county’s 7,994 confirmed cases.