(CNN)Dr. Deborah Birx, the White House coronavirus response coordinator, says current technology makes it impossible to test every American for coronavirus. The United States, she says, will need a "breakthrough" in testing to screen large numbers of people.
Antigen tests: the coronavirus 'breakthrough' that a top White House official says we need
According to Birx, that breakthrough is antigen testing. Often used to check for the flu and strep, antigen tests look for pieces of a virus -- often the proteins that cover its surface.
That differs from most coronavirus tests, which look for the virus' genetic material and require a number of chemicals to operate, many of which are in short supply. The tests can also take hours to run.
Antigen tests are simpler -- and potentially less reliable -- but they can provide results in as little as 15 minutes, according to the US Centers for Disease Control and Prevention.
"There will never be the ability on a nucleic acid test to do 300 million tests a day or to test everybody before they go to work or to school," Birx said earlier this month. "But there might be with the antigen test."
With a potential market of hundreds of millions of tests a day, why doesn't the US already have antigen tests?
For starters, they're not easy to make, and validating their accuracy can be time-consuming and expensive. There also hasn't been a big market for them before now.