It's rare that you can change another persons mind. But you can try to understand why they believe what they do.
You present vaccinations as an example, with "decades of evidence supporting them." That's far less time than evidence supported a flat earth.
The thing is, some vaccines work pretty well. Others don't. It's complicated by the fact that if they don't work, or if they injure or kill you, you can't get your money back or bring lawsuits against the manufacturers or providers.
And there's no laws or regulations that say vaccines must work. Vaccine makers can literally solubilize dog shit and call it a vaccine. And it will "work" for quite a lot of people. There's billions of dollars counting on the us believing they're effective. That blind faith in vaccines has been waning for quite a while now.