It's been about a year since the coronavirus pandemic started to take hold in the United States. Recently, NPR science correspondent Rob Stein has been talking to infectious disease experts, epidemiologists, public health officials, medical historians and for the first time, many are cautiously offering hope. They say the worst may be finally over — but factors like vaccination rates, changes to public health policy and variant resistance to vaccines could upend that recovery.Reach the show by emailing shortwave@npr.org.