By Shankar Vedantam
Washington Post Staff Writer
Thursday, September 4, 2008
A common vaccine given to children to protect them against measles, mumps and rubella is not linked to autism, a study published yesterday concludes.
The findings contradict earlier research that had fueled fears of a possible link between childhood vaccinations and a steep increase in autism diagnoses. In February 1998, the Lancet journal published a study by British researcher Andrew Wakefield of 12 children with autism and other behavioral problems that suggested the onset of their behavioral abnormalities was linked to receiving the MMR (measles, mumps, rubella) vaccine.
The new study comes as the U.S. Court of Federal Claims in Washington is in the midst of evaluating evidence on whether children's vaccines are implicated in causing autism. A special master is evaluating three different kinds of claims -- two of which specifically link the MMR vaccine with autism.
Like Wakefield's study, the new study looked for evidence of potential links between MMR vaccinations, autism and the digestive (gastrointestinal, or GI) problems sometimes seen in autistic children.
"If in fact you want to implicate a factor in the causation of an illness, it must be present before the illness," said W. Ian Lipkin, a professor of epidemiology, neurology and pathology at Columbia University, explaining the idea behind the study. "In the event MMR was responsible for autism, the MMR must precede the onset of autism."
"There was no evidence . . . MMR preceded either autism or GI problems" in the children studied, he said.
The research, published in the journal Public Library of Science One, examined when the children began showing behavioral problems and when they were vaccinated, and it examined bowel biopsies for telltale genetic traces of the MMR vaccine. Since obtaining the biopsies required sedating the children and an invasive procedure, Lipkin said his analysis was limited to a small sample of 38 children who needed the biopsies as part of their medical care.
The researchers studied the biopsies for traces of measles virus RNA. Where a 2002 study had found traces of the measles virus in a high percentage of biopsies taken from autistic children, the new study did not -- and also found no difference in the biopsies of children who were autistic and children of similar age who were not.
Lipkin said the theory linking MMR vaccine to autism involves a chain of events where the live virus in the measles vaccine would grow in the intestinal tract, cause inflammation and trigger formation of toxins that would affect the central nervous system.
If the dramatic results reported in the earlier research were accurate, Lipkin and his coauthors said, they should have found traces of measles RNA in bowel biopsies of a large proportion of the autistic children. Instead, they found such traces in just one child who was autistic and one child who was not.
Patient advocate Rick Rollens, who is convinced that vaccines caused his son to become autistic, said the new research had been rigorously conducted. Rollens, who co-founded the MIND Institute at the University of California at Davis, which studies autism and other neurodevelopmental disorders, praised the study for highlighting the importance of gastro-intestinal problems among autistic children, but he predicted it would not put the controversy to rest.
"This study has addressed one of many theories" about how vaccines might be linked to autism, Rollens said. "This study by itself does not exonerate the role of all vaccines."
Larry Pickering, a pediatrician and immunization expert at Emory University and the Centers for Disease Control and Prevention in Atlanta, said the 1998 study and others had prompted some parents to forgo vaccinating their children.
In the first eight months of 2008, he said, 91 percent of the 131 children diagnosed with measles in the United States had not been vaccinated against the disease or had uncertain vaccination status.
"Often these children will cluster," he said. "If a measles case comes into this cluster, this virus is very easily transmitted. The clustering of people without protection against measles is doubly worrisome."