Overview of Vaccines & Autism

Vaccines are generally considered to be the most successful public health intervention ever devised. And yet there have been opponents of vaccines ever since there have been vaccines. So-called antivaccinationists have claimed over the years that vaccines do not work, despite the overwhelming evidence that they do. They often spread misinformation about vaccine, such as the notion that vaccines weaken the immune system, when in fact they work by strengthening the immune response against the target infection.

In recent years the antivaccine movement has focused on the claim that vaccines are linked to neurological injury, and specifically to the neurological disorder autism, now referred to as autism spectrum disorder (ASD). However the scientific evidence overwhelmingly shows no correlation between vaccines in general, the MMR vaccine specifically, or thimerosal (a mercury-based preservative) in vaccines with ASD or other neurodevelopmental disorders.

The primary argument made for an association between thimerosal and ASD is that the rate of diagnosis of ASD has been steadily increasing since the early 1990s. At that time also the routine vaccine schedule was increasing, resulting in an increasing total dose of thimerosal. The antivaccinationists then assume causation from correlation to blame rising ASD rates on thimerosal.

However, by 2002 thimerosal was completely removed from the routine vaccine schedule, and now remains only in some flu vaccines. The total dose of thimerosal exposure is far below 1990 levels, before ASD diagnoses began to rise. Antivaccinationists predicted that ASD rates would fall dramatically in the years following the removal of thimerosal from most vaccines – but rates have continued to rise without even the slightest change in the rate of increase. This is a powerful refutation of the thimerosal-autism hypothesis, and has been replicated in other countries.

Further, the best epidemiological evidence suggests that the rise in the diagnosis rate of ASD is an artifact of broadening the definition of autism, diagnostic substitution, and increased surveillance. Therefore there isn’t really an autism “epidemic” just a change in the definition and efforts to make the diagnosis.

Undaunted, the antivaccinationists have changed their claims to blame any number of “toxins” in vaccines. However, their claims have no scientific validity.

From Science-Based Medicine. With permission.