In their peer group they have many very unhealthy people and seen a lot of friends die. Some died from botched unnecessary medical interventions or were causalities of medical bureaucracy or malpractice. Some have also been screwed over significantly by government authorities at different points in their lives. This leads to hesitancy and skepticism for new treatments, and authorities.

That is to say, they need to be convinced that the health authorities promoting vaccines now are different from the ones that promoted treatments that killed their peers. They need to be convinced that the same government authorities promoting or requiring vaccines are now more trustworthy than when they fucked them over in the past.

This isn't necessarily a good reason with respect to the vaccine, but I hope it helps you relate