Special Episode: Dr. Ali Khan, Dean of the University of Nebraska's College of Public Health, and a 23-year veteran of the CDC, has traveled the globe investigating infectious diseases like SARS and Ebola. As part CNBC’s “Healthy Returns: The Path Forward” series, he shares the lessons that past outbreaks can teach us about Covid-19, how other countries’ approaches to containing the disease have succeeded, and the challenges that we may still face even after a vaccine is developed.