Vaccines

I am all for vaccines and am getting my daughter vaccinated when she makes her way into this world. I believe if there is a deadly disease out there that can be prevented then freaking prevent it! I wouldn't know what to do with my self if my baby girl died. BUT this is why I'm posting, my twin sister has decided not to vaccinate my niece and my nephew and it scares the shit out of me. I worry about them. And as my twin we usually alwayssss agree on these types of things but her boyfriend strongly believes in not vaccinating them. Can some one PLEASE explain to me why it's a good thing not to vaccinate your children. I really want to understand where my sister is coming from. I'm not judging anyone I just want to understand another point of view. NO HATE COMMENTS!