For the majority of anti-vaxxers its called Confirmation Bias.
https://www.psychologytoday.com/ca/b...firmation-bias
Basically ignore or shout down any evidence to the contrary and hold on to anything that confirms their bias, regardless of quality or preponderance of evidence to the contrary.
My wife had a major allergic reaction to the Flu Vaccine and has had an allergic reaction to some antibiotics. We are not calling for a ban on those things. She just can't have them and rely on the rest of the world using herd immunity to hopefully protect her. There was nothing wrong with the treatments, just her body couldn't take them.