Is there evidence that the MMR vaccine causes autism?
As the parent of three young children, my wife and I have had to wrestle through all kinds of childhood health issues. One that has received a great deal of press lately is vaccination. Many organizations insist that vaccinations are not only unnecessary, but extremely dangerous. On the other hand, other organizations insist that vaccinations are extremely safe and prevent all kinds of serious diseases, both in our own children and in the population at large. Who is right?
In this essay, I'd like to take a look at the arguments on both sides of the debate regarding one issue in particular: is there evidence that the measles, mumps, and rubella (MMR) vaccine causes autism? For many people, the recommendation of their pediatrician is enough. They view the anti-vaccination movement as a fringe group and may even mock them as uneducated and dangerous. However, I don't think that view is charitable. As a Christian, I believe many ideas which are rejected by many people and even by experts, like the existence of God or the possibility of miracles. Although I think I have good reasons for my beliefs, this fact makes me unwilling to simply dismiss any theory merely because it is marginal or unpopular. I want to hear the actual arguments on both sides and weigh them to the best of my abilities. Although the evidence can and should include the testimony of people who are deemed to be experts in that field, 'expert opinion' cannot be the only evidence presented.
With that said, let's consider the question of whether the MMR vaccine causes autism. I will examine the original paper that prompted that claim along with later research. I'll then discuss some of the controversy surrounding the original paper and its primary author, Dr. Andrew Wakefield, and will conclude by asking how we should form views on controversial topics. But first, I want to begin with a discussion of evidence.
What counts as evidence?
When I began this research, I first had to answer a question of methodology: how would I test the claim that 'the MMR vaccine causes autism'? For example, imagine that I were a new father completely unaware of any controversy surrounding the MMR vaccine. Where would I look to find out whether the MMR vaccine is safe or unsafe? Presumably, I would not want to listen to only one side of the debate. If I insisted that all anti-vaccine websites or newsletters or publications were dishonest and were only in it for the money, then it would be impossible for me to fairly evaluate the information they presented. In the same way, we could not fairly evaluate the safety of vaccines if we insisted that all pro-vaccine information was merely propaganda from Big Pharma. Both of these positions have cut themselves off from any verification or fact-checking. Instead, we have to include as many sources as we can and weigh the actual evidence presented in them. We may conclude after the fact that certain sources are biased, but making this assumption in advance renders it impossible to ever investigate the claims by various organizations. Therefore, in deciding the question of whether the MMR vaccine causes autism, I will consider both sides as impartially as I can, not immediately dismissing either as hopelessly biased, but testing each claim and then drawing conclusions on the basis of the evidence gathered.
We should also be wary of personal experience. Obviously, we have to trust personal experiences to some degree. If my daughter tells me that she gets a headache when she eats chocolate, I don't ask for independent evidence because the claim she is making is about her own experience; it is not a universal claim about all other people. On the other hand, if my daughter says, "I get headaches when I eat chocolate; therefore, everyone gets headaches when they eat chocolate and you should stop eating chocolate," I would point out that she can't validly draw that conclusion. In the same way, there are many sincere, generally trustworthy people who have had very positive or very negative experiences with essential oils or gluten or organic produce or vaccines. But we cannot assume that their personal experiences reflect universal truths about all people, especially in the case of medicine, where individual circumstances can greatly affect outcomes.
The original study
The claim that the MMR vaccine causes autism originated with a 1998 paper published by Dr. Andrew Wakefield and 12 co-authors in the prestigious British medical journal The Lancet. Interestingly, this paper explicitly states, "We did not prove an association between measles, mumps, and rubella vaccine and the syndrome described." Although the paper does suggest that the MMR vaccine 'might' be related to autism, it closes with the caution that, "[f]urther investigations are needed to examine this syndrome [regressive autism] and its possible relation to this vaccine." So what is the actual claim made by the paper, and on what evidence is it based?
The 1998 Lancet paper put forward two hypotheses: first, that regressive autism might be caused by or related to some intestinal dysfunction and second that this intestinal dysfunction might be caused by the MMR vaccine. These two claims were originally based on the study of 12 children who displayed both behavioral regression (for example, loss of language skills) and intestinal problems. In 8 of these 12 children, behavioral regression was linked to the MMR vaccination "either by the parents or by the child's physician." In these eight children, the paper reported that behavioral symptoms occurred very soon after vaccination, roughly 6 days on average. The children were also found to have abnormal intestinal function. Given these findings, especially the short time between the MMR vaccination and the claimed onset of behavioral symptoms, the suggestion that the MMR vaccination may have had something to do with regressive autism does not appear unreasonable. However, in a press conference immediately after the release of the Lancet paper, Dr. Wakefield was asked: "Are you saying now then that there does appear to be a proven link between the vaccine and the side effects?" He replied, "No, the work certainly raises a question mark over MMR vaccine, but it is, there is no proven link as such and we are seeking to establish whether there is a genuine causal association between the MMR and this syndrome or not. It is our suspicion that there may well be but that is far from being a causal association that is proven beyond doubt." As with any scientific finding, particularly one relying on a very small set of only twelve patients, further investigation was necessary before any solid claim could be made about the link between the MMR vaccine and regressive autism. To the best of my knowledge and after searching the scientific literature, this is still the only scientific study which posits a connection between the MMR vaccine and autism.
So what did follow-up studies show?
If anyone reading this essay has questions about it, feel free to e-mail me at Neil -AT- Shenvi.org. If you're surprised that an evangelical Christian would appeal to evidence and reason, please take a look at some of the links I provided at the end of this essay. I also highly recommend the book The Reason for God by Tim Keller. It is phenomenal. Free sermons treating many of the topics covered by this book can be found here.