Dr. Deborah L. Birx said the U.S. had entered a “new phase” in the fight against the virus, and urged people to consider wearing masks at home. With a focus on the coronavirus, other deadly diseases are making a comeback. Dr. Deborah L. Birx said the U.S. had entered a “new phase” in the fight against the virus, and urged people to consider wearing masks at home. With a focus on the coronavirus, other deadly diseases are making a comeback.