Autism and MMR Vaccine Safety
Other recent investigations show no causal relationship between MMR (or other
measles-containing vaccines) and either
autism or inflammatory bowel disease.
In 1999, the Working Party on
MMR Vaccine of the United Kingdom's Committee on Safety of Medicine evaluated several hundred reports, collected by lawyers of people with autism,
Crohn's disease, and similar disorders that were supposedly developed after receiving the MMR or MR vaccine. The Party acknowledged that it was impossible to prove or refute the suggested associations because of variable data quality, biased selection of cases, and lack of a control group. However, after a systematic, standardized review of parental and physician information, the Working Party concluded that the information available did not support the suggested causal associations or give cause for concern about the safety of MMR or MR vaccines.
Another study published in
Lancet by Taylor and colleagues provides population-based evidence that overcomes a number of limitations that the Working Party and the Wakefield group experienced. The authors identified all 498 known cases of
autism spectrum disorders (ASD) in children living in certain districts of London who were born in 1979 or later and correlated the cases to an independent vaccination registry. (ASD includes classical autism,
pervasive developmental disorder, not otherwise specified [
PDD-NOS] or atypical autism, and
Asperger syndrome.) The results of this study were as follows:
- The authors showed that the number of ASD cases has been increasing since 1979, with no jump after the introduction of the MMR vaccine in 1988.
- The authors found that children who were vaccinated before 18 months of age were diagnosed with autism at ages similar to children who were vaccinated after 18 months of age, indicating that the vaccination did not result in earlier expression of ASD characteristics.
- The authors discovered that at age two, the MMR vaccination coverage among ASD cases was nearly identical to vaccination coverage of children in the same birth cohorts in the whole region, providing evidence of a lack of overall association between the ASD and the vaccination.
- Taylor and colleagues established that the first diagnosis of autism or initial signs of behavioral regression were not more likely to occur within time periods following MMR vaccination than during other time periods. However, parental concern clustered at six months post-vaccination.
The results of the study were similar when cases of classical autism were analyzed separately.
In 1997, the National Childhood Encephalopathy Study (NCES) examined any possible link between measles vaccine and neurologic events. Researchers in England found no indication that the measles vaccine contributes to the development of long-term neurological damage, including educational and behavioral deficits.
Another study also showed no evidence of association between the MMR vaccine and autism. The study compared autism prevalence rates in populations of children from two communities in Sweden (prior to 1982). The results indicated no difference in autism prevalence between children born after the introduction of the MMR vaccine in Sweden and those born before the vaccine was used.
Several other published epidemiological studies show no causal association between MMR vaccination and autism or inflammatory bowel disease, including retrospective studies that showed no association between the rates of autism and vaccine coverage in young children, and prospective studies of vaccine associated adverse events. Other studies have reported no increased risk for inflammatory bowel disease in children vaccinated with MMR. Additional studies are under way.
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