My dad is trying to push his antivaxx views on me.

I have a 6 month old son who is vaccinated. I have always had a great relationship with my dad and I have always respected his opinion until I had a child. Anytime I mention something about DS other than perfectly normal things, my dad jumps to vaccines. I don't have the guts to stand up for vaccines to him because he does a lot for our family and is otherwise a great dad and grandpa. We have, up until this point, avoided the vaccine conversation but he continues to bring it up. Has anyone else dealt with this? What should I do? via /r/Parenting http://ift.tt/2AHlL1Q