University of Michigan
Department of Pediatrics
Evidence-Based Pediatrics Web Site

Question

• The mother of a 20 year old male with autism is wondering if the MMR vaccination he was given at 15 months may have caused his disease.  Is there any association between autism and MMR?

Clinical Bottom Lines

1. A case series based statistical study fails to show any increased incidence in autism with MMR vaccination introduction, and no higher rates of autism in those vaccinated vs.unvaccinated.
2. Fear of autism is not a statistically valid reason to forego MMR vaccination.
3. The reason for the rise in prevalence of autism is not clear, but the MMR vaccine is not the culprit.

Summary of Key Evidence

1. 498 children with autistic spectrum disorders were identified in the NE Thames region of England.
2. Immunization information from a computerized data base were obtained on these children.
3. In a Poisson regression analysis, no step up in the incidence of autism were noted for those born after the initiation of the MMR vaccine in 1988.
4. The age at diagnosis of autism was compared for those immunized, unimmunized, and with late vaccination.  No change in the age of diagnosis was detected.
5. Using the case series model derived by Farrington, no temporal association was found in the diagnosis of autism and the MMR vaccine. 
6. The case series model is applicable when the overall incidence of disease is low.

Additional Comments

• The prevalence of autism continues to rise, and no clear reason for this increase is known.
• The case series analysis allows for study of rare events without a cohort, while allowing similar power.  It requires the assumption that the disease in question is rare.

Citation

1. Taylor B, Miller E, Farrington CP, Petropoulos MC, Favot-Maynaud I, Li J, Waight P. Autism  and measles, mumps, and rubella vaccine: no epidemiological evidence for a causal association. Lancet 1999; 353(9169):2026-2029.
2. Farrington CP, Nash J, Miller E. Case series analysis of adverse reactions to vaccines: A comparative evaluation. American Journal of Epidemiolog, 1996; 143(11):1165-1172
3. DeStefano F, Chen RT.  Negative association between MMR and autism. Lancet 1999; 353(9169): 1987-1988.
4. Farrington CP. Relative incidence estimation from case series for vaccine safety evaluation. Biometrics 1995; 51: 228-235.

CAT Author: Laura Kisloff, MD

CAT Appraisers: John Frohna, MD

Date appraised: February 21, 2000