A large-scale study has added to a growing body of research absolving the childhood vaccine for measles, mumps, and rubella from causing the national spike in autism over the past decade.
Some parents who have agonized over what may have caused their children’s autism—a complex neurological disorder that impairs the ability to communicate and form relationships—not surprisingly eyed the MMR vaccine. After all, the symptoms in autistic children often start appearing by age 2, which happens to be when youngsters get that shot.
Danish researchers, in the most exhaustive study to date, found that children who had the immunization were no more likely to develop autism than those who had not been vaccinated. Over the years, smaller studies likewise have downplayed the connection between vaccines and autism.
The new study, published this month in the New England Journal of Medicine, looked at the health records of 537,303 children—every child born in Denmark between 1991 and 1998. Of those children, 82 percent had received the MMR vaccination, identical to one given in the United States.
Scientists at the Danish Epidemiology Science Center found that 316 children from that total population had been diagnosed with autism, and another 422 were diagnosed with disorders along the autism spectrum. The rate of autism was virtually the same for children who had received the vaccine and those who had not.
Scientists also looked at when the children were diagnosed with autism in relation to when they got the immunization. They found no correlation between the timing of the vaccination and the onset of autism symptoms.
“This study provides strong evidence against the hypothesis that MMR vaccination causes autism,” the study says.
Educators across the United States have seen large increases in the number of students identified as autistic. Twenty years ago, between two and five cases of autism were reported per 10,000 people nationwide. Now, the disorders have been identified as affecting as many as one in 500 people, making it more common than childhood cancer or Down syndrome.
But nobody knows exactly why the increase has occurred, and studies frequently raise more questions than they answer.
In another recent study, researchers at the University of California, Los Angeles, have pinpointed a region of the human genome—specifically, on chromosome 16—that may contain the risk gene for attention deficit hyperactivity disorder. That same chromosome has previously been shown to contain the risk gene for autism.
Researchers said the coincidence may mean that ADHD and autism have common genetic underpinnings. But they do not yet know whether the same gene contributes to both disorders.
“This study provides compelling evidence that ADHD and autism may have a lot more in common than we ever thought,” said Dr. Susan Smalley, the principal investigator for the study and a co-director of the Center for Neurobehavioral Genetics at the UCLA Neuropsychiatric Institute. “It is also quite feasible that distinct risk genes underlying each condition just happen to be next to each other.”
Though there is no cure for autism, children who receive appropriate early treatment, including educational intervention, can show great improvement, and in some cases go on to lead relatively normal lives. Providing such treatment has put a financial strain on some school districts, however.
Meanwhile, even with the Danish study, vaccines have not been fully exonerated. Some experts believe the problem may not be the vaccines themselves, but instead may be thimerosal, a mercury-based vaccine preservative. Exposure to too much mercury can cause brain damage in developing brains.
In 1999, the federal Food and Drug Administration said babies who receive the series of recommended immunizations are exposed to more mercury than the U.S. Environmental Protection Agency considers safe. At that time, FDA officials asked vaccine manufacturers to stop using thimerosal. Some batches of the vaccines containing thimerosal are still in circulation, however, as manufacturers have been left to phase out the preservative voluntarily.
Still, the Danish study seems to have reassured some parents, who worried they had made the wrong choice for their children by getting the MMR vaccination.
Roberta Buckberg, of Olney, Md., the mother of a 4-year-old son who has Asperger’s syndrome, a disorder that falls on the autism spectrum, said when she heard the news on the radio, she practically cheered.
“We have tormented ourselves with ‘what ifs,’” she said. “By far the worst ‘what if’ has been the vaccination one. ... If we have another child, would we vaccinate? But, aware of the fact that an unvaccinated child cannot attend public school, and that the diseases the vaccines prevent can be life-threatening, we would probably vaccinate all over again.”
A version of this article appeared in the November 20, 2002 edition of Education Week as New Study Discounts Autism-Vaccine Linkage