For months, public health experts have been eagerly watching the companies developing spit tests for the coronavirus that could be used at home, producing results in a matter of minutes.

If these rapid tests worked, they could greatly expand the number of people tested. Some experts have said they could perform as well as a vaccine in curbing the spread of the virus. But so far, the technology is not panning out as some have hoped.

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

“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, an E25Bio founder and its chief executive. The notion that the virus sets up shop in the mouth and produces enough antigen to be picked up by today’s technology, he said, “is far-fetched.”

The two companies pursued saliva for months. But as researchers continued to tinker with their tests, both companies found saliva’s performance to be more lackluster than anticipated.

Despite a deluge of data on saliva’s benefits, it’s relatively new to the testing scene. No fully government-approved test for a respiratory pathogen has ever used spit.