LA County Replicates Stanford Santa Clara Serology: About As Lethal As Seasonal Flu

LATimes |  Hundreds of thousands of Los Angeles County residents may have been infected with the coronavirus by early April, far outpacing the number of officially confirmed cases, according to a report released Monday.

The initial results from the first large-scale study tracking the spread of the coronavirus in the county found that 4.1% of adults have antibodies to the virus in their blood, an indication of past exposure.

That translates to roughly 221,000 to 442,000 adults who have recovered from an infection, once margin of error is taken into account, according to the researchers conducting the study. The county had reported fewer than 8,000 cases at that time.

The findings suggest the fatality rate may be much lower than previously thought. But although the virus may be more widespread, the infection rate still falls far short of herd immunity that, absent a vaccine, would be key to return to normal life.

Antibody tests, also known as serology testing, have increasingly become a focal point in the response to coronavirus because they can potentially show the true extent of the virus’ reach and therefore can shed light on how close the population is to achieving herd immunity. That occurs when enough people have some degree of immunity to the virus that it becomes difficult for infections to spread.

“Any way you slice the data ... it’s clear that herd immunity in this situation does not apply. It’s still way below that level,” said Natalie Dean, a professor of biostatistics at the University of Florida.

Such tests can also provide a more accurate picture of how lethal the virus is.

The mortality rate is based on the number of confirmed infections; the higher the number of infections, the lower the fatality rate. Both studies estimated a mortality rate of 0.1% to 0.2%, which is closer to the death rate associated with the seasonal flu.