Ask the parents of autistic children whether they believe childhood vaccines can cause autism, and the answer will probably be yes. They have heard of too many cases of babies who were perfectly normal until they got their measles, mumps and rubella (MMR) shot and then within weeks — if not days — started throwing tantrums, losing language skills and generally tuning out.
Ask doctors the same question, and they are likely to cite the panel of experts convened by the Institute of Medicine last year. It studied the evidence but found no explanation for how vaccines might possibly cause autism. Included in the review were studies that showed no significant difference in the incidence of autism disorders before and after MMR immunization became routine in 1988 in the United Kingdom. “We bent over backward to look for the biological mechanisms that would support a link,” says the panel’s chairwoman, Dr. Marie McCormick of the Harvard School of Public Health.
But failing to prove that something can happen is not the same as proving it doesn’t, and the issue is still a matter of furious debate. The only scientific evidence against childhood vaccines comes from Dr. Andrew Wakefield, formerly at the Royal Free Hospital in London. His theory is that autism stems from a severe immune reaction to something in the vaccine. In February he published a paper showing that immunized children with autism and bowel disorders have higher levels of measles particles in their intestinal tissue than normal children do. The evidence is not entirely persuasive, however; measles particles in the tissues do not necessarily mean that the virus — or the vaccine — causes autism.
What about all the children whose symptoms appeared shortly after their MMRs? The association may be purely coincidental. The shots are given at 15 months, which is when behavior and speech patterns in babies usually become sufficiently pronounced for parents to start noticing that something is wrong. Most of the evidence suggests that autism is primarily a genetic disorder. It may be that some symptoms appear immediately after birth but are too subtle to be spotted in the first year or so of life.
To get more definitive answers, the National Institutes of Health and the Centers for Disease Control have each launched their own investigations. Karyn Seroussi of Poughkeepsie, N.Y., for one, supports this research. “If it’s the shots, I want to know,” says the autism advocate and parent of an autistic son. “If it’s not, I want to know what the heck it is that’s causing autism.” On that, both parents and doctors can agree.