Some “anti vaccinationist” think that vaccines don't work and they just weaken the immune system and cause neurological injury.
They believe that vaccines cause autism in young children. Autism can develop with a combination of genetic and environmental influences, and some genes associated with autism are found in people who are not autistic. Vaccines causing autism has not been proven because there are many factors that go into the development of the disorder. Illnesses such as smallpox and polio are prevented by vaccines. Although no child is born with these illnesses, the likelihood for unvaccinated children to contract them is higher than children that have been vaccinated.