Watch live: Dr. Anthony Fauci, optimistic about the COVID-19 vaccine, he and health officials say Trump did not ask to delay testing

Since Fauci last testified, hospital doctors have become more skilled in treating coronavirus patients with the techniques and medications available to them. The United States continues to increase testing, with some 27.5 million Americans, or more than 8% of the population, evaluated so far. But most communities still lack enough trained health workers to track contacts, the job of identifying people who have had interactions with an infected person. That could make it more difficult to control emerging outbreaks.