Vaccination passports are coming, its just a matter of time. It wont be a paper card, it will be in digital form. Whether you realize it or not, your vaccination details are all logged in a data base. The WHO is working on co ordinating each countries database, so that those who need to access such information such as airlines, employers etc etc can do so. So like what currently happens with ESTA, when you check in for your your flight, it shows whether or not you have ESTA. We can not complete check in without a valid ESTA. When we get checked by USA Homelands security on arrival to USA and our passports are scanned, again the ESTA information is shown to the agent.