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Am Fam Physician. 2005;72(3):517-518

A suggested link between measles, mumps, and rubella (MMR) immunization and autism and other developmental delays has led to a decrease in immunization for infants. The rate of MMR coverage in England fell from 92 percent in 1996 to 82 percent in 2003. Outbreaks of measles followed this reduction. The adverse publicity was based on a study of 12 children with pervasive developmental problems and gastrointestinal symptoms. These children were reported to have fragments of measles virus in their intestinal tissue. It was suggested that MMR immunization could trigger certain types of developmental delay, including autism. Although many subsequent studies consistently failed to confirm any association between MMR immunization and developmental delay, public confidence has been slow to recover. Smeeth and colleagues conducted a large case control study to investigate any association between MMR immunization and developmental delay.

They used the United Kingdom General Practice Research Database (GPRD) to identify individuals born after 1973 who had been diagnosed with pervasive developmental disorders (PDDs), including autism and Asperger’s syndrome. Patient records were reviewed for evidence to confirm the diagnosis. For each of the 1,294 confirmed cases, up to five control patients without diagnosis of PDD were selected who were the same age, gender, and attended the same family practice. Immunization data were extracted on the 1,294 patients and the 4,469 patients in the control group.

Most of the patients (76.6 percent) were diagnosed as having autism. Patients visited general practitioners more frequently before the diagnosis of PDD than the control group. The median age of PDD diagnosis was 5.4 years. The unadjusted odds ratio for MMR immunization and diagnosis of PDD was 0.73. After adjustment for age of joining the general practice database, this increased to 0.86. Analyses by age of immunization and other variables did not significantly change the odds ratios (see accompanying table). The odds ratios consistently failed to show any positive relationship between MMR immunization and diagnosis of PDD or autism.

MMR vaccination before index dateUnadjusted OR (95 % CI)Adjusted OR (95 % CI)*P (for adjusted OR)
At any age
No MMR vaccination(1.0)
Vaccinated with MMR0.73 (0.59 to 0.91)0.86 (0.68 to 1.09)0.21
Before and after third birthday
No MMR vaccination(1.0)
MMR vaccination before third birthday0.75 (0.60 to 0.95)0.90 (0.70 to 1.15)0.39
MMR vaccination after third birthday0.68 (0.50 to 0.94)0.77 (0.55 to 1.08)0.13
Before and after 18 months of age
No MMR vaccination(1.0)
MMR vaccination before 18 months0.76 (0.60 to 0.96)0.90 (0.70 to 1.15)0.39
MMR vaccination after 18 months0.69 (0.54 to 0.89)0.80 (0.61 to 1.05)0.11

The authors conclude that MMR immunization is unrelated to the risk of being diagnosed with PDD or autism. Because data on immunization were recorded before diagnosis of PDD, recall bias was unlikely. These results correlate with three other trials studying the risk of PDD or autism following MMR immunization. From these studies and their own results, the authors calculate a pooled relative risk of 0.87 percent. They argue that no convincing evidence links MMR immunization to developmental disorders and call for urgent research into the etiology of autism and other developmental disorders.

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