A new study from USC and Los Angeles County health officials showed that more people countywide have been infected with the novel coronavirus than previously projected, and the death rate is lower than originally reported.
The study’s lead investigator Neeraj Sood, a professor of health policy and vice dean for research and faculty affairs at the USC Price School of Public Policy, said the results help identify the virus mortality rate and generate a better understanding of the pandemic.
Most studies conducted so far focused on those who have severe symptoms of the virus. Not that many studies have looked at individuals who may have had the virus and recovered.
In its first round of testing, medical experts conducted rapid antibody testing of 863 residents at six drive-through centers.
They tested blood from COVID-19-positive patients with a 90 to 95% accuracy rate. USC validated those tests in a small sample at a lab at Stanford University, according to the university.
Results showed that roughly 4.1% of the county’s adult population has developed antibodies to the virus, which is an indication they are or were infected at some point.
Adjusting the findings for statistical margin of error showed that about 221,000 to 442,000 adults in the county have had the infection–– 28 or 55 times more than previously recorded.
In a frequently asked questions article published on the USC media website on April 16, Sood also touched on the topic of herd immunity–– a concept of indirect protection from diseases, which stems from a large community of immune individuals.
Herd immunity is achieved when 60% of the population carries antibodies, either through past infection or vaccination, according to Sood, but it is not yet known for sure that COVID-19 antibodies create immunity.
LA County Public Health Director Barbara Ferrer said the figures also show that with thousands of residents likely infected and capable of transmitting the virus, social-distancing requirements need to remain in place.
“These results indicate that many persons may have been unknowingly infected and at risk of transmitting the virus to others,” Ferrer said. “These findings underscore the importance of expanded polymerase chain reaction (PCR) testing to diagnose those with infection so they can be isolated and quarantined, while also maintaining the broad social distancing interventions.”
The findings also showed that the mortality rate of COVID-19 is lower than previously thought. As of press time, 600 deaths have been reported countywide.
Dr. Paul Simon, chief science officer at LA County Department of Public Health, who co-led the study, said that although the report shows a lower death rate, “the number of COVID-19 related deaths each day continues to mount.”
Aside from mortality rates and infections, Sood said the study can also help officials see the effects of social-distancing orders and other restrictive measures.
According to Sood, if there is a cluster of ZIP codes where people say they are not doing social distancing compared to one that is, over time, officials would expect to see the epidemic curve flattening in ZIP codes where social distancing is practiced.
According to a LA County Public Health press release, antibody testing will continue over time on a series of representative samples of adults to determine the scope and spread of the pandemic across the county.
The test participants were selected via a proprietary database maintained by LRW Group, a market research firm, according to the press release.