New Stanford research concludes that an estimated 2.5% to 4.2% of Santa Clara County residents carry antibodies to the COVID-19 virus, revealing that the pathogen is far more widespread than earlier estimated.
This startling finding suggests that between 48,000 and 81,000 people were infected in Santa Clara County by early April, between 50 and 85 times higher than the number of confirmed cases at that date.
“The most important implication is that the number of infections is much greater than the reported number of cases,” concludes the research paper, published Friday morning in the “preprint” medRxiv.
“Our estimate also suggests that, at this time, a large fraction of the population remains unexposed in Santa Clara County,” it adds.
The news comes at a time when health experts and elected officials are embracing immunity as a potential end point to the pandemic. It is not yet known if antibodies prevent future infection. If so, antibody protection would offer people a safe route out of strict “sheltering.”
The research also implies that the death rate is far lower than believed. At the time of research, 69 county residents had died – a fatality rate, based on estimated infections, of only 0.12 to 0.2%. California’s assumed death rate, based only confirmed cases, is 3%.
These results represent the first large-scale community-based prevalence study in a major U.S. county completed during the rapidly changing pandemic, using newly available test kits.
The project, led by Dr. Eran Bendavid, an infectious disease specialist and professor of medicine with Stanford Health Policy, shows whether someone has been infected by the virus in the past. They used a random population sample, a standard method for determining true population exposure to a virus.
In contrast, COVID-19 virus testing only tests people with significant symptoms. It does not measure the true number of people who have been infected by the virus, many of whom have no symptoms or very mild symptoms.
Santa Clara County resident Rich Altmaier welcomed the news, saying it could be the key to getting our lives and economies back on track.
“This data from Stanford showing a low fatality rate, together with what we have learned about the virus attacking older people with pre-existing medical conditions, and quite mild for the young, tells us: shelter the old and pre-conditions, and everyone else can go on,” said Altmaier of Cupertino.
“The question has always been: who needs to be isolated? Why everyone?” he said. “I have been in heartsick fear for the number of people with no income, no savings, and soon no food. Our shutdown is a terrible, terrible burden. The sheltering of the old remains important, so indeed strong protections are needed. But so much easier to achieve if we focus on, say, those over age 65 or with pre-conditions.”
Several other teams worldwide have also started testing population samples. Like Stanford, they’ve found that there’s a large underestimate of infections.
Reports from the Italian town of Robbio, Italy, where the entire population was tested, suggest at least 10% rate of infections. A survey in the western Germany municipality of Gangelt, highly affected by illness, found a 14% positive rate.
A UC Berkeley project, which will begin in May, will test a large and representative swath of 5,000 East Bay residents. Scientists will take saliva, swab and blood samples from volunteers between the ages of 18 and 60 around the region. The Colorado town of Telluride — and soon, the Marin County town of Bolinas – also plan antibody testing.
Stanford’s hospitals are currently testing healthcare workers. Within two months, the university says it will offer tests to the general community.
In the U.S., a multiyear project supported by the Centers for Disease Control and Prevention is already collecting samples from blood donors in six major urban areas to create a picture of nationwide antibody prevalence.
The Stanford researchers caution that while their prevalence estimates are representative of the situation in Santa Clara County as of early April, other regions are likely to have different estimates based on social distancing policies, outbreak progression and other localized factors.
They tested 3,330 people on April 3 and April 4 at three locations spaced across Santa Clara County — two county parks in Los Gatos and San Jose, and a church in Mountain View — to gain a snapshot of how many people in the county had already been infected, but weren’t seriously sick and didn’t realize it.
“This is critical information,” said principal investigator Bendavid, in an April 3 interview.
Repeated serologic testing in different geographies, spaced a few weeks apart, could create a broader picture of the extent of infection over time, he said.
The wide range in estimates — 2.5% to 4.2% — is based on what’s known about the performance of the test kit, made by Minnesota’s Premier Biotech. Its sensitivity and specificity would push the number higher or lower.
The team’s protocol was informed by a World Health Organization protocol for population-level COVID-19 antibody testing.
Because volunteers were disproportionately white and female, relative to the county’s demographics, the team’s data scientists had to make statistical adjustments. Those imbalances were addressed by giving less computational “weight” to white women. Latino and Asian volunteers, who were overrepresented, got greater “weight.”
There are other potential biases. The research may have favored people in good health who could drive to a testing site, or those with prior COVID-like illnesses who wanted antibody confirmation.
Like all other emerging COVID-19 research papers, the work is published in the “preprint” medRxiv, so has not been peer reviewed. (Conventional publication can take as long as a year.) Santa Clara County Department of Public Health holds the copyright on the paper.
Until now, we’ve underestimated the prevalence of the illness because our current virus testing started too late, missing cases, according to the researchers. Viral testing also misses people who are newly recovering from infection – or, significantly, people who have few or no symptoms.
The test measures so-called “neutralizing antibodies,” which are proteins that prevent infection by binding to the part of a virus that latches onto and enters a person’s cell. It then hijacks the cell’s genetic machinery to make millions of copies of itself.
These are the same cells that COVID-19 survivors are donating to Bay Area blood banks in an effort to save sick patients.
Now researchers are scrambling to answer two questions: Do these antibodies protect against reinfection?And how long do they persist?
In an ideal world, the antibodies for COVID-19 would act like those for chicken pox, providing lifetime immunity.
Early research suggests a more complicated picture, clarified by time, global cooperation — and more Stanford-like tests.
Read the study: https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v1
