If you read the internet sites where anti-vaccine activists post regularly, one fact that sticks out is that most of the criticisms of the host of scientific studies that cast doubt on a link between vaccines and autism focus on vary narrow areas of analysis. For instance, whenever a new study is published that reinforces the scientific consensus on autism and vaccines, there is a barrage of criticisms regarding the methodology and conclusions of the individual study rather than a reasoned analysis of the totality of the study in the context of the weight of scientific evidence, with the study limitations being part of the story.

Researchers generally don’t try to hide the flaws in their studies; their scientific colleagues tend to point them out if not disclosed by the authors. All studies have flaws. They involve a series of trade offs made by the study’s authors who weigh (sometimes unsuccessfully) factors like size, expense, design, time period, accuracy, completeness and many others. Any study in isolation will likely be largely meaningless due to the limitations of each study. However, that does not mean those studies are not valuable, particularly when combined with other studies on the same topic that involved different trade offs. And, more importantly, this obsession with the details of individuals studies, along with the other minutia that are constantly being debated, serve to distract the debate from the big picture.

For instance, relating to thimerosal, once you get out of the trees and start surveying the forest, you start to notice that thimerosal has been largely withdrawn from numerous western countries with high levels of autism, including Canada, Denmark, the UK, Sweden and the US. This withdrawal has occurred at different times over the last 20 years. And, in each country in which thimerosal has been withdrawn, autism rates have continued to increase. This fact has been documented in numerous studies that I discuss in my section on thimerosal. And, those who implicate thimerosal in autism have not provided any studies that provide contradictory epidemiological evidence. You can debate the biomechanics of thimerosal in the brain all day long, and watch thimerosal interact with cells in test tubes, and inject thimerosal into the brains of rats for years and make interesting observations, but this does not cancel out the fact that autism levels have not been shown to correlate in any way to thimerosal exposure. And, that is really the most important question related to whether thimerosal causes autism.

Another example of missing the big picture involves global rates of autism and vaccinations. The number and type of vaccines vary from country to country around the world. Massive variation also occurs in the years during which vaccines were introduced. The DPT vaccination is pretty common today. The Rotavirus vaccination is pretty rare. Some countries introduced MMR in the 1960’s. Some countries still don’t give all three vaccinations (or any of the three), and some that do now only started doing so in the last decade. Some countries still use multi-dose vials with thimerosal; some countries have shifted to single dose vials without thimerosal for almost all vaccines.

If vaccines are responsible for all or most, or even many, cases of autism, you would expect a pattern to develop related to autism cases and vaccination rates, from country to country or year to year. Instead, what we have seen is a steady increase in apparent prevalence, which trend exists globally as far as we can see. And, autism is present at relatively high levels in all kinds of different countries, from Mexico to the United Arab Emirates to Sweden to Japan. Autism is present in developed and developing nations, in western and eastern countries, in predominantly Muslim and Christian countries, and in the north and south hemispheres. Any claim that a single factor (such as vaccines) is causing autism is logically specious because of the diversity of the exposures that humans across the planet experience. At best, vaccines can be one small part of a very complicated causal picture. However, this is not a view that is advocated by those who advocate that vaccines cause autism.