Autism and measles, mumps, and rubella vaccine: no epidemiological evidence for a causal association

Background. We undertook an epidemiological study to investigate whether me asles, mumps, and rubella (MMR) vaccine may be causally associated with aut ism. Methods. Children with autism born since 1979 were identified from special needs/disability registers and special schools in eight North Thames health districts, UK. Information from clinical records was linked to immunisatio n data held on the child health computing system. We looked for evidence of a change in trend in incidence or age at diagnosis associated with the int roduction of MR IR vaccination to the UK in 1988. Clustering of onsets with in defined postvaccination periods was investigated by the case-series meth od. Findings. We identified 498 cases of autism (261 of core autism, 166 of aty pical autism, and 71 of Asperger's syndrome). In 293 cases the diagnosis co uld be confirmed by the criteria of the International Classification of Dis eases, tenth revision (ICD10: 214 [82%] core autism, 52 [31%] atypical auti sm. 27 [38%] Asperger's syndrome). There was a steady increase in cases by year of birth with no sudden "step-up" or change in the trend line after th e introduction of MMR vaccination. There was no difference in age at diagno sis between the cases vaccinated before or after 18 months of age and those never vaccinated. There was no temporal association between onset of autis m within 1 or 2 years after vaccination with MMR (relative incidence compar ed with control period 0.94 [95% Cl 0.60-1.47] and 1.09 [0.79-1.52]). Devel opmental regression was not clustered in the months after vaccination (rela tive incidence within 2 months and 4 months after MMR vaccination 0.92 [0.3 8-2.21] and 1.00 [0.52-1.95]). No significant temporal clustering for age a t onset of parental concern was seen far cases of core autism or atypical a utism with the exception of a single interval within 6 months of MMR vaccin ation. This appeared to be an artifact related to the difficulty of definin g precisely the onset of symptoms in this disorder. Interpretation. Our analyses do not support a causal association between MM R vaccine and autism. If such an association occurs, it is so rare that it could not be identified in this large regional sample.