Q: What have studies found regarding MMR vaccine and autism?
A: Studies have shown no relationship between MMR vaccination in children and development of autism. For example, researchers in the U.K. studied the records of 498 children with autism born between 1979 and 1998. They found:
- The percentage of children with autism who received MMR vaccine was the same as the percentage of unaffected children in the region who received MMR vaccine
- There was no difference in the age of diagnosis of autism in vaccinated and unvaccinated children
- The onset of "regressive" symptoms of autism did not occur within two, four or six months of receiving the MMR vaccine
Q: Are there studies that suggest there might be a connection between autism and the MMR vaccine?
A: The existing studies that suggest a causal relationship between MMR vaccine and autism have generated media attention. However, these studies have significant weaknesses and are far outweighed by other studies that have consistently failed to show a causal relationship between MMR vaccine and autism.
One 1998 study by Wakefield and colleagues brought the MMR-autism theory to the forefront. Wakefield reviewed reports of children with bowel disease and regressive developmental disorders, mostly autism. The researchers suggested that MMR vaccination led to intestinal abnormalities, resulting in impaired intestinal function and developmental regression. This hypothesis was based on 12 children. In nine of the cases, the child's parents or pediatrician speculated that the MMR vaccine had contributed to the behavioral problems of the children in the study. There are a number of limitations in the Wakefield study: