The results of a large new study in the journal Pediatrics show no relation between the combined vaccination against measles, mumps, and rubella (MMR) and the development of autism.
In 2001, a panel of experts convened by the US Institute of Medicine, Washington, DC, rejected the contention that vaccination with MMR caused autism, on the basis of overall data at a population level. The panel did, however, encourage additional studies to assess the possibility that a few children might be at increased risk.
Because autism is usually diagnosed during the toddler years, when children receive many childhood vaccinations, some advocacy groups believe that the causes of autism are vaccine related. Many of these groups pointed to thimerosal, a preservative in the MMR vaccine, as a possible culprit. Scientists say it is possible that if it got into the brain, thimerosal could cause brain damage. Although it is no longer used in childhood vaccines in the United States, it remains in the influenza vaccine and in vaccines in other countries.
In the new study, Dr Frank DeStefano from the US Centers for Disease Control and Prevention in Atlanta, Georgia, and colleagues compared the MMR vaccination histories of 624 autistic children and a control group of 1824 school matched, non-autistic children. Vaccination data were abstracted from immunisation forms required for school entry. Records of children who were born in Georgia, Atlanta, were linked to Georgia birth certificates for information on maternal and birth factors (Pediatrics 2004;113: 259-66).
In the study, most of the autistic children (70.5%) and the control children (67.5%) were vaccinated by the recommended age of 12 to 15 months. When the team analysed different age cut offs, they found that similar proportions of case and control children were vaccinated before age 18 months or before age 24 months, when developmental abnormalities are usually recognised.
The data also show no link between receipt of the MMR vaccine and the development of autism in any of the subgroups of children analysed, including those who seemed to be developing normally and then regressed and those who developed up to a certain point and then reached a plateau.