Antibody Study Shows COVID-19 Rate of Infection May Be up to 85 Times Higher Than Reported

A study in a county in California suggests that the prevalence of people infected with the coronavirus is much higher than previously thought, potentially complicating decisions on whether to end widespread lockdowns.

Blood from 3,300 volunteers living in Santa Clara was extracted from a finger prick and analyzed at the start of April. The Stanford University study, which has not been peer reviewed yet and was posted on medRxiv, found that between 2.5 percent of 4.5 percent of people tested positive for antibodies.

Extrapolated over the county's population of two million, the data predicts that between 48,000 and 82,000 people could have been infected with the virus at that time. The upper estimate is more than 80 times higher than the official case count of 1,000.

"Our findings suggest that there is somewhere between 50- and 80-fold more infections in our county than what's known by the number of cases than are reported by our department of public health," Dr. Eran Bendavid, who led the study, told ABC News.

The results also suggested that the upper limit of the coronavirus's mortality rate was only 0.2 percent, much lower than the nationwide death rate of 4.1 percent.

Antibody testing
A clinical test in the Immunology lab at UW Medicine looks for antibodies against SARS-CoV-2 on April 17, 2020 in Seattle. Karen Ducey/Getty Images

However there are considerable caveats with researchers saying that it is not clear whether such results would apply to the rest of the country. Some scientists have also expressed misgivings about the accuracy and reliability of kits used in the studies, Nature reported.

Bendavid pointed out that around 95 percent of the Santa Clara population were still without antibodies and it would be tough to decide whether to ease restrictions because "knowing that well upwards of 90 percent of the population doesn't have antibodies is going to make that a very difficult choice."

Public health officials say widespread antibody tests are instrumental in helping governments decide whether to return populations to work because those tests can help figure out who is less at risk.

The study could point toward the development of herd immunity, although experts insist health policy choices should follow further tests.

"The idea this would be a passport to going safely back to work and getting us up and running has two constraints: we do not know if antibodies protect you and for how long, and a very small percentage of the population even has antibodies," said Arthur Reingold, an epidemiology professor at UC Berkeley, not involved in the study, according to The Guardian.

The graphic below, provided by Statista, shows the growth of COVID-19 cases in three U.S. states.

COVID-19 in NY, Washington, California
The graphic below, provided by Statista, shows the number of confirmed COVID-19 cases, the disease caused by the new strain of coronavirus, in a selection of states.