Your little boy has not had the mmr vaccine (measles, mumps, rubella) because you are apprehensive about vaccines and their side effects. your sister says that you are setting your son up for a potentially damaging scenario. who makes more sense--you or her?

Your sister is thinking more logically in this scenario. Vaccines are proven to help fight the bacteria that causes the diseases mentioned above. Avoiding these vaccines raises a higher chance of contracting the diseases than getting the vaccines does.

Your sister, theres no concrete proof of any side affects of vaccines unless your using an attenuated (live) vaccine on someone who is immunocompromised or has an otherwise weak immune system which depending on the boys age would already have been identified. Not only would not getting the MMR vaccine create risk for an otherwise preventable disease but it also contributes to the endangerment of herd immunity; the concept that if enough people are vaccinated then those who cant get them (ex; immunocompromised people) are still safe from the disease.