As more vaccines roll out, many countries - including the US and the European Union - are looking into digital vaccine passports. New York state recently created a vaccine passport in the form of a smartphone app, called Excelsior. Vaccine passports could make international travel and public indoor gatherings more secure. But there are concerns over privacy and fairness. I spoke to Dr. Arthur Caplan, Medical Ethics expert at NYU’s School of Medicine and asked him first what exactly is a vaccine passport.