In a video by Naomi Wolf, CEO of Daily Clout, an IT firm, she indicates that IF a vax passport were implemented it would be 30 minutes work to turn it into the social score system that they have in China. If you say something against the administration your score goes down. If your score gets too low, you aren't allowed into the grocery store (under the guise of being dangerous due to a virus).
America has unfortunately moved way down the path towards socialism (at least government officials). These passports would be one of the last steps.