Roberto Cauda, professor of infectious diseases of Universita Cattolica del Sacro Cuore in Milan, Italy said that a vaccine passport is essentially a "COVID health certificate" which includes proof that a person has been vaccinated, or other important information regarding their COVID status. With a vaccine passport, travelers could prove they are safe for long-distance travel by rail or air, simply by showing their health certificate on a device. However, countries have different standards and requirements for their vaccine passports.