Many proponents of the idea that vaccines cause autism have a habit of shifting between variants of the autism / vaccine theory without a lot of thought. It seems that they don’t care about exactly how vaccines cause autism, as long as they do. Many of these proponents will daily switch back and forth between the variants of the argument they espouse, including the following as causes of autism: thimerosal, measles virus in the MMR vaccine, the MMR vaccine generally acting through unspecified mechanisms, total vaccine load, aluminum (an adjuvant), formaldehyde (a preservative alternative to thimerosal), ethylene glycol (antifreeze – never shown to actually be in vaccines), a combination of these and other toxins in vaccines, and all of the above but only in susceptible populations.

David Kirby is a classic example of a theory shifter. He is a former AP reporter who became famous in the autism world for writing a book, Evidence of Harm, arguing for the vaccine / autism connection. He also writes extensively on autism on several blogs including Age of Autism, a website that strongly advocates for the presence of an autism epidemic that is caused by vaccines. He was a huge advocate of the thimerosal theory of autism. He was so convinced thimerosal caused autism, he agreed in public on several occasions that autism rates should start dropping in 2007 (or earlier) if thimerosal was really responsible for autism. When definitive data from a California study showed that just the opposite was occurring, David started spending his time covering other variants of the ‘vaccines cause autism’ theory, without ever acknowledging 2007 passing and no reduction in autism incidence. It seems as if his interest is in showing that vaccines cause autism, not in uncovering the truth.

There are several large logical problems with this theory shifting.

First, these variants of the vaccine theory all tend to have very different theoretical mechanisms on how they cause autism. Shifting between these variants involves taking largely contradictory positions at the same time. This is essentially the thought process: okay, it is absolutely clear mercury poisoning from thimerosal causes autism, that autism is a unique form of mercury poisoning; well, okay maybe the evidence is not clear, but it is indisputable that the action of the measles virus in the gut interacting with brain, results in autism as a direct result of immunization with the MMR vaccine; it is also clear that the general immunological challenge presented from ganging together too many vaccines at one time causes autism; also, heavy metal poisoning really is to blame, but it is the aluminum through a mechanism we haven’t identified yet, not the mercury…

Second, each variant of the autism / vaccine theory can stand alone as its own hypothesis. If you test a hypothesis into what causes a disease and it fails, then logic demands that you open the non-answered question of causation to all possibilities. Thus, if you suggest that thimerosal causes autism, and the balance of the scientific evidence proves otherwise, than an intellectually honest person still interested in autism causation would start considering all kinds of causes, particularly ones that have some evidentiary support, such as pesticides or alcohol. But, instead of casting about the world with an open mind looking for potential causes, the vaccine theorists immediately sow suspicion on other wholly unrelated aspects of vaccines, with no good reason at all for their focus since vaccines have never been significantly implicated in autism.

Third, all of the vaccine variants can’t be right. There are tens of thousands, if not more, of possible environmental contributors to autism, from food colorings, to pesticides, to fluorescent lights, to a lack of exercise. It is unlikely that many of them are dominant contributors. And, only a few of them are represented in vaccines. It would be a stretch to imagine a situation in which nearly every substance in vaccines has a substantial contribution to autism, not leaving much of a role for all of the substances and exposures not contained in vaccines, but that we are exposed to in high levels from our food, our water, our air, our senses, and other vectors that don’t involve needles. This is particularly true when we know that there are numerous environmental exposures not associated with vaccines that can contribute to autism development, such as fetal alcohol exposure. It is highly unlikely that all of the vaccine theory variants are correct. And, if some are wrong despite the passionate argument of those who claim they cause harm, what makes anyone think that any are correct?

Fourth, there is just something dishonest in lacking the courage of your convictions. If you really think thimerosal causes autism, stand by your position. Make your assertion, evaluate the evidence, and reach your own conclusion. If you think you are still right, stick by your guns. Don’t just slide over to another position, without acknowledging the abandonment of your prior one. That is just lacking moral courage and is likely indicative of having another motivation other than truth seeking.