A study that tested 863 Los Angeles County residents last month found that 4 percent of them carried antibodies for SARS-CoV-2 — and 60 percent of those who had been exposed to the virus were entirely asymptomatic.
The study was conducted by researchers at USC, and it followed on a similar antibody prevalence study conducted in Santa Clara County in early April. In the earlier study, Stanford researchers found 1.5 percent of the 3,300 county residents tested carried antibodies for the virus, which the team extrapolated to mean that 2.5 to 4 percent of the county at large might have been exposed by that point.
That study was criticized both for the way subjects were found (Facebook ads) and for the potential for false positives in the tests used — as well as for the methodology used in reaching the estimate of 48,000 to 81,000 Santa Clara County residents exposed.
The USC study, as ABC 7 reports, concludes that an estimated 360,000 adults in Los Angeles County might have been exposed to the virus without necessarily knowing it — extrapolating out the result of the small-scale test to the county's 8 million residents.
Los Angeles County has confirmed almost 40,000 COVID-19 cases to date, but this latest study suggests that nine times that number may be closer to the true total.
Still, anything resembling "herd immunity" is still a long ways off, as study lead Neeraj Sood says.
"This is not something that is going to go away in the next month or the next two months," he tells ABC 7. "This is something that's going to be with us for several months or until the time we have a vaccine."
In the good news column, the New York Times reports today that progress is being seen in a global race toward an effective vaccine, with different teams developing vaccines with different methodologies. Just this week we learned that one U.S. team developing a vaccine using a new, mRNA-based technology, has already shown some positive preliminary results.
Related: Large-Scale Antibody Test Suggests As Many As 80,000 Santa Clara County Residents Have Already Had COVID-19