The Delta variant is causing growing concern and upending any hopes that the country can soon return to normal. Every day we are learning more about the Delta strain, including that even vaccinated people may be able to spread it.  While vaccine rates are rising, hesitancy and the political fight over masking are only confounding efforts to rein in Covid. This hour, the latest science and guidance on Covid, the Delta variant, vaccines, and masking with University of Pennsylvania immunologist JOHN WHERRY and New York University School of Medicine infectious disease specialist CELINE GOUNDER.