Johnson & Johnson is the fourth company to begin late-stage human trials here in the U.S. with its covid-19 vaccine candidate. The company is enrolling up to 60,000 volunteers from around the world to be a part of the trial. But unlike the other top vaccine candidates, J&J's vaccine will be administered in just one dose, a potential game changer when and if the vaccine is rolled out to the public. For more, we spoke to Johnson & Johnson's Chief Scientific Officer, Doctor Paul Stoffels.