My best friend from high school, who is still one of my closest and dearest friends is antivax. Also anti microwave, and a few other things. It's actually really hard to deal with, because she and I have always been on the same wavelength about most things. She's smart enough to know the arguments against her point of view, too, but because she had a personal bad experience with vaccines (her eldest got really sick, and it was attributed to the vaccine), she has become somewhat irrational on the point. It's one of the few things I leave alone.