"The Vaccine War" and the problem of spurious correlation

For years there has been a growing controversy between the scientific-medical community which mandates vaccinating all children, and a subculture of parents who oppose vaccinating their children due to fears of a link between vaccines and autism or other ailments*. I just finished watching the Frontline documentary on "The Vaccine War" which provides a nice summary of the view from both sides. Watch the documentary on http://www.pbs.org.

The strongest "evidence" linking vaccines to autism is the tight timeline between receiving vaccines and developing the early signs of autism. Consequently because these two events are linked by time many parents assume a causal relationship. The "post hoc ergo propter hoc" fallacy ("after this, therefore because of this") is well known, but still powerful. In sociology this phenomenon is called a "spurious" correlation. It appears that vaccines and autism are causally linked, but in fact they are both consequences of a child's age. Just before they are 2 years old children receive a large dose of vaccines and at the same age certain developmental problems such as autism begin to manifest.

A friend and I were recently discussing the same logical fallacy with regards to allegations that amniocentesis during pregnancy may lead to miscarriage. However, at all points during a pregnancy and particularly during the first part of pregnancy there is a rate of spontaneous miscarriage. If someone miscarries soon after an amniocentesis they are likely to blame the amniocentesis for the unfortunate outcome. For an overview of this issue see about.com. Whether it is vaccines or miscarriage we like to assign blame when things do not go as planned.

The scientific evidence is strong and compelling that vaccines are in no way related to autism (the primary battle cry of the anti-vaccine movement). The original 1998 study in the British medical journal The Lancet hypothesized that there was a link between the MMR (Measles, Mumps, and Rubella) vaccine and autism was retracted in 2010 amidst allegations of scientific misconduct. See the wikipedia page for a summary of the history of this study and its author Dr. Wakefield. Despite the scientific consensus many people seem to believe that vaccines are linked to autism.

I am doubly interested in this debate as both (1) someone who worked for several years at a non-profit which provided services for people with developmental disabilities, and (2) someone working towards a Ph.D. in sociology with my research focusing on the topic of medical sociology. From the first time I heard that vaccines were being implicated in causing autism I was skeptical. In my professional experience it was immediately noticeable that autism sometimes appears to run in families. In most families only one child is autistic, but there were many cases where multiple siblings would be diagnosed with autism. The CDC's fact sheet on autism suggests a genetic component:

"Studies have shown that among identical twins, if one child has autism, then the other will be affected about 75% of the time. In non-identical twins, if one child has autism, then the other has it about 3% of the time. Also, parents who have a child with an ASD have a 2%–8% chance of having a second child who is also affected." CDC fact sheet on autism, download here.

Although autism is not a straightforward genetic condition (such as Down's Syndrome which can be traced to a chromosomal abnormality), experts now believe that it is likely that genetic predisposition and environmental factors may combine to cause autism.

So why has the controversy about the vaccine-autism link thrived? The Frontline documentary provides a clear answer. Personal anecdotes from individual parents (typically mothers) abound on the internet. Parents share personal stories and come together as a interest group, as the celebrity Jenny McCarthy demonstrates with the organization "Generation Rescue". These personal stories are heartbreaking and powerful, and sadly the scientific evidence against the vaccine-autism link is not presented as succinctly or powerfully. In fact, finding and reading scientific studies online is quite difficult. Many scientific articles are unavailable to the general public, and even after accessing them they can be difficult for a lay person to read and understand. It is also questionable whether the average American understands how the scientific method and epidemiological comparisons constitute evidence against the vaccine-autism link.

I would like to make a final point about the damage caused to people with autism by the allegations that vaccines cause autism. This position assumes that autism is (1) undesirable, (2) preventable, and (3) in some cases reversible (see the Generation Rescue site for more on "recovery" from autism). To me all of these points are suspect. While most people agree that they would rather not have a child with autism (given the choice), people with autism, like any other people fall on a spectrum. There are those with autism who have accomplished great things, for example Temple Grandin. And there is speculation that many famous historical figures may have had what is now called "Asperger's Syndrome". More importantly as I learned in my time working with people with all different types of developmental disabilities they are just like any other people. Some are wonderful people, some I would not like even if they had no disability. Yes, many of these people do require more assistance from family members and public resources, but this is not an argument against their existence. Newborn babies, elderly people, and those with many other medical conditions or disabilities also require great assistance. I feel it does an injustice to people living with autism now to focus on how to prevent and "reverse" autism instead of doing what we can do help people with autism to live more successful lives by focusing on giving them the education and services that enable them to live as independently as possible. In addition, as the Frontline documentary points out, the time and effort spent investigating the vaccine-autism link may have detracted from research into the actual causes of autism.

I believe the controversy over the vaccine-autism link is a result of the uneasy relationship our society has with both medicine and disability. We are simultaneously dependent on modern medicine and skeptical of it dictating how we must live our lives. Many of us are unsure how to conceptualize disability or respond to people with disabilities (perhaps the topic for another blog post). Mental disabilities are sometimes even more confounding to people than physical disability. The combination of our ambivalence toward medicine and disability make autism a topic that will remain controversial.

*A substantial part of the documentary reports on parents who choose not to vaccinate not due to fears about autism per se, but for other philosophical reasons. Perhaps more fodder for a later blog post. Sociologist Jennifer Reich at the University of Denver has conducted research on how opting out of vaccine schedules for children is seen as "good mothering", by a subgroup of women. Her paper on the topic is a fascinating exploration of how mothers view their choice to resist vaccinations.