Trying Autism in the Vaccine Court

Yesterday, 4,800 parents of autistic children got their day in court. The special federal vaccine court is hearing their claims that the mercury-containing vaccine perservative thimerosal is responsible for their children's autism.

As the New York Times notes,

Every major study and scientific organization examining this issue has found no link between vaccination and autism, but the parents and their advocates have persisted…

Thimerosal was almost entirely removed from pediatric vaccines in 2001 after some government scientists expressed concern about the amount of mercury that children who got routine vaccinations would be exposed to. Since then, autism rates in the United States have shown no signs of dropping.

It is true that autism diagnoses have exploded over the past two decades. Why? On Sunday, the New York Times published an op/ed by a professor of social work and an epidemiologist that offered a thoughtful analysis of why diagnoses of autism have been rising so steeply. Of particular interest is this observation:

Urban planners know that "if you build a new road, people will drive on it." Likewise, in special education, if you create a new counting category, people will use it. At the same time, older counting categories may then be used less frequently as our ability to differentiate diagnoses improves. And true enough, our study found that the growth in children classified with autism was accompanied by a corresponding decrease in the number of special education students with other designations.

This is an example of "diagnostic substitution" — as information on new autism classifications has gradually spread, the label "autistic" has been used more commonly for children who previously would have been labeled something else. Our analyses demonstrated that from 1994 to 2003, in 44 of 50 states, the increase in autism was completely offset by a decrease in the prevalence of children considered "cognitively disabled" or "learning disabled."

Some of my earlier reporting on the lack of a connection between vaccines and autism here and here.