MMR and autism
Concerns about a possible link between vaccination with MMR and autism were raised in the late 1990s, following publication of studies claiming an association between natural and vaccine strains of measles virus and inflammatory bowel diseases, and separately, MMR vaccine, bowel disease and autism. WHO, on the recommendation of GACVS, commissioned a literature review by an independent researcher of the risk of autism associated with MMR vaccine; the outcome of the review was presented to GACVS for its consideration.
Autistic spectrum disorder represents a continuum of cognitive and neurobehavioral disorders including autism. The prevalence of autism varies considerably with case ascertainment, ranging from 0.7 – 21.1 per 10 000 children (median 5.2 per 10 000) while the prevalence of autistic spectrum disorder is estimated to be 1 - 6 per 1000. Eleven epidemiological studies (representing the most recent studies, mostly in the last 4 years) were reviewed in detail, taking into consideration study design (including ecologic, case control, case-crossover and cohort studies) and limitations. The review concluded that existing studies do not show evidence of an association between the risk of autism or autistic disorders and MMR vaccine. Three laboratory studies were also reviewed. It was concluded that the alleged persistence of measles vaccine virus in the gastrointestinal tract of children with autism and inflammatory bowel disease requires further investigation through independent studies before the laboratory findings of the published studies, which have serious limitations, can be considered confirmed.
Based on the extensive review presented, GACVS concluded that no evidence exists of a causal association between MMR vaccine and autism or autistic disorders. The Committee believes the matter is likely to be clarified by a better understanding of the causes of autism. GACVS also concluded that there is no evidence to support the routine use of monovalent measles, mumps and rubella vaccines over the combined vaccine, a strategy which would put children at increased risk of incomplete immunization. Thus, GACVS recommends that there should be no change in current vaccination practices with MMR.