A carefully designed study of blood samples from Orange County residents found that 12% had coronavirus antibodies — meaning their immune systems had fought the virus at some point — an infection rate more than seven times higher than official case counts suggest.
“What was most surprising among the researchers was how high the seroprevalence of COVID was,” said Tim Bruckner, a study principal and associate professor of public health at UC Irvine.
The majority of people studied who tested positive had no symptoms, Bruckner said.
While more than 10% of Orange County residents tested over the summer had COVID-19 antibodies, that’s still a long way from “herd immunity,” when so many people have antibodies that the virus runs out of new hosts.
Matt Zahn, medical director of the county Health Care Agency’s Communicable Disease Control Division.
For Bernadette Boden-Albala, dean of UC Irvine’s public health program, an expert in social epidemiology and study principal, it also speaks to the fact that there’s huge variability in how people show symptoms, if at all.
The disproportionately high rates of tests returning positive in the county’s hot spots have been tamped down by the Orange County Health Care Agency in partnership with nonprofit groups like Latino Health Access, Boden-Albala said.
Such campaigns have brought more testing and resources to neighborhoods where many residents can’t work from home and have little access to health care.
Case data — drawn from sick people who wind up at diagnostic testing sites, clinics and hospitals — peg the COVID death rate at about 10% for those 65 and older in Orange County.
The widespread prevalence of COVID in Orange County warrants continued public health measures, the study said: physical distancing, proper and consistent use of face masks, ventilation and hand hygiene.
And, in addition to contact tracing, county health authorities “may want to consider active surveillance of novel infections.” That would involve some 800 to 1,000 tests per week in a representative sample of residents, as well as a targeted component for higher-risk groups or places such as nursing home residents, laborers in high-density settings and highly impacted neighborhoods.
Neeraj Sood, professor of public policy at the USC Price School for Public Policy and principal investigator for the groundbreaking serology study done by USC and the Los Angeles County Department of Public Health in the spring, said that’s one of the outstanding questions.
“The level of antibodies you have, and how fast they decline, might correlate with how severe your disease was,” said Sood, who’s also planning to study people who’ve tested positive over time in L.A.
A big takeaway from O.C.’s work is that many people had COVID and didn’t know it, supporting the notion that the virus is a silent spreader, said UCI’s Bruckner
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