I’ve looked into this before and I’m pretty sure the expected harm from an adverse reaction to some (many?) vaccines outweighs the expected harm from actually getting the disease it protects against (because the chance of an adverse reaction from eg. the polio vaccine is much higher than the chance you’ll actually get polio). I’d add that as another reason why people would be against personal vaccination, and it’s understandable.
Matthew Barnett says:
https://www.facebook.com/mati.roy.09/posts/10158690001894579