As far as vaccinating people with very weak immune systems, it would be practical to use a killed virus vaccine and not a live attenuated one. However, the whole point of a person with a weak immune system is that they don't produce normal levels of antibodies, so vaccinating them is probably an exercise in futility, if you think about it.
People who are in a severely deficient nutritional state probably don't have the energy to spare to mount an immune response, but I expect it would have some success.
Wakefield has been refuted, but he got more press than the ones who did the refuting, and so it has gone on and on. Thimerosal or no thimerosal, the autism rate has gone upward at a dizzying rate. As Orac noted, autism is on the rise even in countries that don't use thimerosal-treated vaccines. If it is an environmental thing, there must be more of it in Japan than here in the US. We know so little about autism that it is hard to say definitively that any one thing is a cause.
http://www.cbsnews.com/news/for-children-with-autism-brain-abnormalities-may-begin-in-utero/New evidence suggests that the brains of autistic children have structural differences when compared to the brains of non-autistic children. Research suggests these changes are present by the second or third trimester of pregnancy. It would be hard to show any effect of thimerosal at that stage of development.
