If the statistic one in 166 has a familiar ring, perhaps that's because you recently heard it on a television commercial or read it in a magazine. According to widely publicized estimates, one in 166 is now the proportion of children who suffer from autism. This proportion is astonishingly high compared with the figure of one in 2,500 that autism researchers had accepted for decades. Across a mere 10-year period--1993 to 2003--statistics from the U.S. Department of Education revealed a 657 percent increase in the nationwide rate of autism.
Not surprisingly, these bewildering increases have led many researchers and educators to refer to an autism epidemic. Representative Dan Burton of Indiana also declared in 2001 that we have an epidemic on our hands. But what's really going on?
Before we explore this question, a bit of background is in order. Autism is a severe disorder that first appears in infancy. Individuals with autism are characterized by problems with language, social bonding and imagination. All suffer from serious communication deficits, and some are mute. They do not establish close relationships with others, preferring to remain in their own mental worlds.
They engage in highly stereotyped and repetitive activities, exhibiting a marked aversion to change. About two thirds of autistic individuals are mentally retarded. For reasons that are unknown, most are male.
The causes of autism remain enigmatic, although studies of twins suggest that genetic factors play a prominent role. Still, genetic influences alone cannot account for such a rapid and astronomical rise in a disorder's prevalence over a matter of just a few years. As a consequence, investigators have turned to environmental factors for potential explanations. The causal agents proposed include antibiotics, viruses, allergies, enhanced opportunities for parents with mild autistic traits to meet and mate, and, in one recent study conducted by Cornell University researchers, elevated rates of television viewing in infants. Few of these explanations have been investigated systematically, and all remain speculative.
Are Vaccines the Problem?
Yet one environmental culprit has received the lion's share of attention: vaccines. At first blush, vaccines would seem to make a plausible candidate for the source of the epidemic. The debilitating symptoms of autism typically become apparent shortly after age two, not long after infants have received vaccinations for a host of diseases. Indeed, many parents claim that their children developed autism shortly after receiving inoculations, either following a vaccine series for mumps, measles and rubella (German measles)--the so-called MMR vaccine--or following vaccines containing thimerosal, a preservative that contains mercury.
Much of the hype surrounding a link between vaccines and autism was fueled by a widely covered investigation of 12 children published in 1998 by British gastroenterologist Andrew Wakefield and his colleagues. The study revealed that symptoms of autism emerged shortly after the children received the MMR vaccine. (Ten of the 13 authors have since published a retraction of the article's conclusions.) Public interest in the vaccine-autism link was further stoked by the provocatively entitled book Evidence of Harm (St. Martin's Press, 2005), written by investigative journalist David Kirby, which was featured in an extended segment on NBC's Meet the Press.
Yet recently published research has not been kind to this much ballyhooed link. The results of several large American, European and Japanese studies demonstrate that although the rate of MMR vaccinations has remained constant or declined, the rate of autism diagnoses has soared. In addition, after the Danish government stopped administering thimerosal-bearing vaccines, the rates of autism continued to rise. These studies and others summarized by the Institute of Medicine suggest there is little evidence that vaccines cause autism. It is possible that vaccines trigger autism in a small subset of children, but if so that subset has yet to be identified.