The Reason Companies Have Ruled Out Rapid At-Home Spit Tests

Saliva does not provide as accurate a measure of Covid's presence because, at least in part, the mouth is not really where the virus implants itself.

 Katharine Wu reports in the New York Times:

Two companies trying to develop rapid at-home coronavirus tests, have abandoned efforts to use saliva samples with their products. Instead, their tests, which detect pieces of coronavirus proteins called antigens, will rely for now on shallow nose swabs. "It’s very difficult for antigen-based testing to work on saliva samples. Saliva’s performance is more lackluster than anticipated. Spit differs from one person to another, and can change over the course of a single day. The notion that the virus sets up shop in the mouth and produces enough antigen there to be detected by today’s technology “is far-fetched.”

The technology for rapid saliva-based coronavirus tests that could be used at home is not panning out the way some have hoped.

E25Bio and OraSure, two companies trying to develop rapid at-home coronavirus tests, have abandoned efforts to use saliva samples with their products. Instead, their tests, which detect pieces of coronavirus proteins called antigens, will rely for now on shallow nose swabs.

Public health experts are eagerly watching the companies trying to develop the technology, which they hope will greatly expand the number of people who are tested. Some experts have even said that the rapid antigen tests, which are aimed at delivering a result in a matter of minutes, could perform as well as a vaccine in curbing the spread of the coronavirus and paving a path back to normalcy.

“If I was placing a bet — which I am, because I’m leading an antigen-based testing company — I would say it’s going to be very difficult for antigen-based testing to work on saliva samples,” said Bobby Brooke Herrera, chief executive of E25Bio and one of its founders. He said the notion that the virus sets up shop in the mouth and produces enough antigen there to be detected by today’s technology “is far-fetched.”

As they continued to tinker with their tests, researchers at both E25Bio and OraSure found saliva’s performance to be more lackluster than anticipated, and were forced to pivot. One problem is that spit differs vastly from one person to another, and can even change over the course of a single day.

Both E25Bio and OraSure now plan to seek authorization from the F.D.A. to sell at-home antigen tests using nose swabs, a technique similar to the one used by the much-talked-about Abbott antigen test that takes about 15 minutes.