Concern over a possible link between the measles, mumps, and rubella (MMR) vaccine and autism has led to a number of retrospective and prospective studies; however, none has confirmed an association. The World Health Organization and other groups have called for further investigations on a population-based scale, which would have more statistical power to detect a possible link. Madsen and colleagues present data from a retrospective cohort study of more than 500,000 children born in Denmark between 1991 and 1998.

The MMR vaccine was used in Denmark beginning in 1987, and the national vaccination program recommended that children be vaccinated at 15 months and 12 years of age. The MMR vaccine used in Denmark contained the same vaccine strains as the U.S. version. Vaccination data were obtained from the Danish National Board of Health, and diagnoses of autism were obtained from the Danish Psychiatric Central Register, which tracks all psychiatric treatment centers in Denmark.

Within a study cohort of 537,303 subjects, 440,655 children received the MMR vaccine. Follow-up data were lost for 5,028 children because of death or emigration during the study period. The mean age at the time of the first dose of MMR vaccine was 17 months, and 98.5 percent of those vaccinated received their first dose before three years of age. Among children who developed autism, the mean age at diagnosis was four years and three months, while other autistic-spectrum disorders were first diagnosed at a mean age of five years and three months.

No association was detected between MMR vaccination and the development of autism or other autism-spectrum disorders. The researchers also found no association between the development of autistic disorder and the age at vaccination, time elapsed since vaccination, or time of year the vaccination was performed. After adjusting for potential confounders, such as age, sex, calendar period, socioeconomic status, birth weight, gestational age at birth, and mother's education level, only age was found to have affected the study findings.

The authors conclude that in this population-based study no association was demonstrated between MMR vaccination and later development of autism.