Although no one has any idea, I think that we are going to go back to the future. Many of us remember having to carry Yellow Fever certificates in order to travel between various parts of the World. While something that those in the "West" may have never dealt with they were a regular part of travel and were WHO, etc approved. I envision a modern adaptation of that whereby when people are vaccinated with approved vaccines in an approved way and properly logged by a national authority that they will probably have the option for either a card based certification or perhaps some sort of smart/number/locator/authenticator.