Autism and measles-mumps-rubella vaccination - Controversy laid to rest?

It has been suggested that vaccination, particularly with measles-mumps-rub ella (MMR) vaccine, may be related to the development of autism. The main e vidence for a possible association is that the prevalence of autism has bee n increasing at the same time that infant vaccination coverage has increase d, and that in some cases there is an apparent temporal association in whic h autistic characteristics are first noted shortly after vaccination. Altho ugh the prevalence of autism and similar disorders appears to have increase d recently, it is not clear if this is an actual increase or the result of increased recognition and changes in diagnostic criteria. The apparent onse t of autism in close proximity to vaccination may be a coincidental tempora l association. The clinical evidence in support of an association derives f rom a series of 12 patients with inflammatory bowel conditions and regressi ve developmental disorders, mostly autism. The possibility that measles vac cine may cause autism through a persistent bowel infection has generated mu ch interest, since it provides a possible biological mechanism. Epidemiolog ical studies, however, have not found an association between MMR vaccinatio n and autism. The epidemiological findings are consistent with current unde rstanding of the pathogenesis of autism, which has a strong genetic compone nt and in which the neurological defects probably occur early in embryonic development. It seems unlikely that a vaccination that is given after birth could cause autism. A minority of cases of autism may have onset after I y ear of age (regressive autism), but the single epidemiological study that i ncluded such cases did not find an association with MMR vaccination. Curren tly, the weight of the available epidemiological and related evidence does not support a causal association between MMR vaccine, or any other vaccine or vaccine constituent, and autism.