Regarding measles, there are four groups of people.
All are represented in my family.
First, the MMR vaccine results in immunity for most who receive it. Two doses provides protection that can be confirmed with blood titers. My wife is in this group.
Second, about 3% of fully vaccinated children do not develop a lasting immune response. They have low blood titers and are not protected against measles. If exposed, this group will likely get the illness. I am in this group. I was thankfully not exposed.
Third, we have the unvaccinated. My son, Eli, is ten months old. He is too young to received the MMR vaccine and thus has no protection. Whether by refusal or because they are too young, exposed unvaccinated children have a 90% chance of getting measles.
Fourth, there are children like my Maggie. These are child who can’t be vaccinated. Children who have cancer. Children who are immunocompromised. Children who are truly allergic to a vaccine or part of a vaccine (i.e anaphylaxis to egg). These children remain at risk. They cannot be protected … except by vaccinating people around them. In August of 2014, Maggie was diagnosed with pre-B acute lymphoblastic leukemia, a form of childhood leukemia. We have been fighting leukemia since then.