Health experts say the country is days away from widespread coronavirus antibody testing.Instead of detecting the virus itself, the tests detect proteins called antibodies that the immune system generates to fight COVID-19. These tests could also determine who has contracted the disease and recovered.Public health experts hope that mass screening with antibody tests could eventually help track how the virus spreads and who might have built up immunity.Dr. Anthony Fauci, the nation's leading infectious disease expert, said the U.S. is days away from having a large number of antibody tests available."But they need to be validated," he said during a CNN interview Friday. "You need to make sure they're consistent and that they're accurate."The FDA is permitting companies to launch certain types of finger-prick tests that can detect whether people may have recently been infected.At Stanford, researchers have already begun testing more than 3,000 people."I think this [study] has very important implications for how we understand the epidemic, for how we move it forward," Stanford's Dr. Eran Bendavid told ABC News' Diane Sawyer. "From our survey really the most important piece of information is, how many people in our country have been infected?"Warner Thomas, CEO of the New Orleans-based Ochsner Health System, and Ochsner's chief medical officer, Robert Hart, also said they expect antibody testing to be available in a couple of weeks."We look forward to being one of the first centers in the country that will be doing antibody testing," Thomas said during a telephone news conference Thursday.It was not immediately clear how many tests would initially be available.