Cognitive dissonance occurs when a behavior (taking vax) goes against beliefs (cognition) which causes stress and creates motivation for people to change either their behaviors or beliefs to regain alignment. In this case since you cannot un-take the vax, it is motivating a change in beliefs. This week known phenomenon was validated experimental by Festinger and Carlsmith as far back as 1959.

“Forced Compliance Behavior When someone is forced to do (publicly) something they (privately) really don't want to do, dissonance is created between their cognition (I didn't want to do this) and their behavior (I did it).

Forced compliance occurs when an individual performs an action that is inconsistent with his or her beliefs. The behavior can't be changed, since it was already in the past, so dissonance will need to be reduced by re-evaluating their attitude to what they have done. This prediction has been tested experimentally”

Link in post.