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 it 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?
Given the tremendous potential public-health significance of a link between the MMR vaccine, a number of scientists immediately followed Dr. Wakefield's suggestion to make a "further investigation" of the purported link between the MMR vaccine and autism. Let me list and describe a few of the more prominent papers:
- In 1999, just a year after the initial Wakefield paper, The Lancet published an article from Dr. Brent Taylor and 6 co-authors which examined a much larger group of patients: 498 individuals diagnosed with autism drawn from a special-needs register in the UK. Although they found a steady increase in the incidence of autism in the overall population, they found no sudden increase in the rate of autism after the introduction of the MMR vaccine in 1988. They also reported that there was "no difference in age at diagnosis between the cases vaccinated before or after 18 months of age and those never vaccinated" and that there was "no temporal association between onset of autism within 1 or 2 years after vaccination with MMR."
- In 2001, three years after the Wakefield study, an article was published in the New England Journal of Medicine on a huge group of 537,303 children from Denmark. After adjusting for factors such as gender and birth weight, the relative risk of a diagnosis of autism for vaccinated children was 8% lower than for unvaccinated children. Similarly, the adjusted relative risk for a diagnosis of autism-spectrum disorders for vaccinated children was 17% lower than for unvaccinated children. Additionally, there was no significant clustering of autism diagnoses in any particular interval after vaccination.
- In 2008, another small study which attempted to replicate Dr. Wakefield's original study was published in PLoS ONE. In it, 25 children with autism and gastrointestinal disorders were compared to a group of children with gastrointestinal disorders alone. The researchers found that "[gastrointestinal] symptom and autism onset were unrelated to MMR timing [i.e. when the MMR vaccine was administered]" stating that "This study provides strong evidence against association of autism with ... MMR exposure."
- In 2014, an analysis of all the published scientific evidence collected so far on the association of vaccines with autism was published by researchers at the University of Sydney, analyzing data from 10 studies which included over 1 million individuals. They concluded that "There was no relationship between vaccination and autism", "There was no relationship between vaccination and ASD (autism spectrum disorder), and "there was no relationship between [autism/ASD] and MMR."
These are only a few of the more prominent studies on this subject. A more extensive list can be found here or here. These studies found no evidence that there is a link between the MMR vaccine and autism and provide positive evidence that withholding the MMR vaccine from children has no effect on autism rates.
Criticism of the original study
So what accounts for the contradictory results of Dr. Wakefield's original study and the follow-up studies I've discussed? A number of scientists have asked that question. Two scientific objections seem the most relevant to me. First, the original study included an incredibly small number of children-- only 12. No matter how compelling the results, medical and scientific studies need to be repeated on large groups to ensure that observations are not due to coincidence. The discrepancies between Dr. Wakefield's 1998 study and later studies could be due in part to the far larger numbers considered in the later studies, which were simply less subject to statistical error. Second, the first study relied heavily on self-reporting from parents regarding the timing of the onset of behavioral regression. But this is an unreliable guide. For example, if you are a parent, can you remember at what age each of your children took their first step? Said their first word? Read their first book? I'd imagine that my own guess might be accurate only to within a few months; it certainly would not be accurate to within a few days or weeks. Consequently, it's questionable whether the timing between the MMR vaccination and the onset of behavioral symptoms could be ascertained accurately merely by asking the parents. At best, we'd have only their best guess.
Another possibility is, of course, that the follow-up studies were wrong. The primary difficulty with this assertion is that the methodology employed in other studies was far more rigorous than Dr. Wakefield's. First, they included far more children, so if we doubt the statistical significance of their results, it seems we would have to doubt Dr. Wakefield's results even more. Second, they relied on far more objective measures of reporting: clinical diagnoses of autism by professionals, vaccination dates, government records, etc. While these methods are also subject to error, they seem less susceptible to error than simple recollection, often many months or years after the fact. A more common explanation is that the follow-up studies were all influenced, either consciously or unconsciously, by the pharmaceutical industry. Given that vaccines are a highly lucrative business, scientists have a financial incentive to produce results that exonerate large pharmaceutical companies, the same companies which award many of the research grants that fund these same medical researchers. As I said at the outset, I'm not denying that this is a possibility. Bias is real and scientists are no less susceptible to temptation than any of us. But I also stated that I would not assume bias at the outset, prior to considering the evidence. Now that we've discussed the evidence, let's consider the possibility of a comprehensive, systemic bias. I don't think that this bias is a legitimate possibility for several reasons:
First, the breadth of the papers I've cited above make comprehensive, systemic bias unlikely. The research I presented was not produced by a single research team or in a single journal or using data from a single country. Instead, they represent a large number of studies all published in extremely prestigious journals from researchers all over the world. To suggest that all of this research was manipulated by Big Pharma requires more than one or two isolated instances of fraud; it would require a vast conspiracy among scientists, journal editors, referees, and governmental health organizations. Second, this kind of comprehensive, systemic bias makes it hard to explain how Wakefield's study was published in the first place. If Big Pharma really has such sweeping influence over all of these various medical journals and the media, how did the Lancet end up publishing his article and why did the media initially greet it with such publicity? Third, the market recalls of highly lucrative drugs makes it untenable to claim that Big Pharma has a stranglehold on the medical literature. For example, in recent years, drugs such as Fen-Phen (1997), Rezulin (2000), Baycol (2001), and Vioxx (2004) have all been recalled by the FDA due to safety concerns that were exposed by clinical studies. But if Big Pharma has the power to silence or marginalize any scientific study which threatens their profits, why would they have failed to do so in these cases? Note that I am not denying here that there is a 'Big Pharma' lobby, that it is powerful, and that it -like any other lobby- can engage in unethical and even reprehensibly evil practices. I'm merely pointing out that it is not very plausible to explain all the evidence I've presented with an appeal to this kind of vast conspiracy.
Next, since we are trying to remain objective, we need to consider the alternative possibility: what if there was a bias on the part of Dr. Wakefield or his coauthors which could account for the discrepancies between his initial study and later studies? Here, I want to try to be as sensitive and as charitable as I can. I will not draw any firm conclusions about Dr. Wakefield's character or motivations. Those are obviously largely beyond my (or anyone else's) grasp. I am merely asking us to consider the information at our disposal with some attempt at dispassionate objectivity.
As many probably know, subsequent to the publication of his original article, Dr. Wakefield was subject to the longest trial in the history of the UK's General Medical Council (GMC), which oversees the certification of doctors who practice medicine in England much like the National Board certifies all doctors licensed to practice medicine in the United States. (Note that the trial was not convened to determine whether Dr. Wakefield's research was correct; scientists and doctors mistaken in their research claims are not always liable to censure. Instead, the GMC was investigating charges that Dr. Wakefield had engaged in unethical medical practices.) In 2010, Dr. Wakefield was found guilty of numerous charges and was stripped of his right to practice medicine in the U.K. Let's consider four of the most troubling charges below.
First, Dr. Wakefield was accused of several unethical practices in the course of his research. For example, Dr. Wakefield took blood samples from children at his son's birthday party. A video of Dr. Wakefield confirming this incident, during which he states that two of the children fainted and one vomited, is available here. The GMC also concluded that several of the 12 autistic children enrolled in the study were subjected to invasive and painful procedures such as colonoscopies that were contrary to their medical interests. The final GMC report included multiple instances where Dr. Wakefield had failed to apply for and obtain permission from the Ethics Committee to carry out various procedures on his patients. If the GMC was correct in finding Dr. Wakefield guilty, these charges constitute a major violation of medical ethics, which has very strict rules regarding the use of human subjects in medical experiments.
Second, investigation by the GMC brought to light several instances of financial conflicts of interest. In 1996 -two years before the publication of the Lancet study- Dr. Wakefield and a lawyer named Richard Barr were awarded £ 57,750 by the Legal Aid Board to support research attempting to prove that the MMR vaccine was causing injury to children, as part of lawsuit against pharmaceutical companies. The autistic children eventually enrolled in Wakefield's study were also litigants in the lawsuit, meaning that if Dr. Wakefield's research was successful, the children would be more likely to win their lawsuit. Dr. Wakefield did not report this conflict of interest either to the Ethics Committee or to the Lancet when his paper was published. Six months prior to the publication of the Lancet study, Dr. Wakefield also filed an application for a patent on a new measles vaccine that he claimed to have invented which would replace the MMR vaccine then in use. Additionally, over the next 9 years, Dr. Wakefield received £ 400,000 from the same lawyers as a consultant in their lawsuit. The facts that Dr. Wakefield received hundreds of thousands of pounds from anti-vaccine lawyers and that his research subjects were involved in an anti-vaccine lawsuit at the time of his study constitute a tremendous financial conflict of interest.
Third, a lengthy investigation into the individual children enrolled in Dr. Wakefield's original study suggested that many of them had exhibited autistic symptoms prior to their MMR vaccination, but that the data were altered to suggest a connection between the MMR vaccine and autism. The entire report can be found here. Fiona Godlee, the editor-in-chief of the British Medical Journal which commissioned the investigation, concluded that while "[i]t's one thing to have a bad study, a study full of error... in this case, we have a very different picture of what seems to be a deliberate attempt to create an impression that there was a link by falsifying the data." Problems with the original study led 10 of Dr. Wakefield's 12 coauthors to retract their interpretation of the data in 2004, and led the Lancet to retract the paper entirely in 2010.
Now, as I have said, I have no desire at all to speak definitively about Dr. Wakefield's motivation. The main question before us is whether, given this information, it is more likely that the numerous, independent researchers who found no link between the MMR vaccine and autism are wrong or whether it is more likely that Dr. Wakefield's original study was wrong. I urge readers who are unsure about the credibility of the claims made above to click through the links I've provided, which come from various news outlets, medical journals and licensing boards. Of course, it is possible that all of these sources are either accidentally incorrect or are deliberately deceiving the public. But one must again consider which is the more likely explanation: that all major news agencies are controlled by Big Pharma, along with all major scientific publications and governmental health agencies? Or that Dr. Wakefield's original study was wrong?
The question of whether or not to vaccinate our children is a weighty one and -unfortunately- not one that we can avoid. Given the importance of this decision, I wanted to discuss the evidence we have at our disposal so that parents can make an informed decision about what is in the best interest of the child. From the evidence I've gathered so far, it seems that an extremely strong case can be made that the MMR vaccine does not lead to autism. First, the original study that prompted this concern insisted that 1) it had not proven a link between the MMR vaccine and autism and 2) stated that follow-up research was needed to test their claims. Yet no subsequent study was able to duplicate Dr. Wakefield's results, and numerous other studies found no link between MMR vaccination and autism. Second, muitiple independent studies by different researches at different institutions showed that unvaccinated children have just as great a risk of autism as vaccinated children. This piece of evidence, to me, is the most compelling. If the MMR vaccine causes autism, then shouldn't we expect to see a significantly lower rate of autism in children who were left unvaccinated? And if we don't, can we really argue that leaving our children unvaccinated will lower their risk of autism? Third, I pointed out that Dr. Wakefield's original study had been retracted from The Lancet and that 10 of his 12 co-authors had withdrawn their support from it's claim that vaccines and autism were linked. It is hard to explain the journal's retraction and the withdrawal of Dr. Wakefield's coauthors if the original study was scientifically sound. Finally, I mentioned that Dr. Wakefield lost his license to practice medicine in England over breaches of medical ethics, and that he had received tens of thousands of pounds from lawyers seeking a link between the MMR vaccines and autism. Now, obviously, this conflict of interest by itself doesn't prove that the study's results were incorrect. But, taken together with all of the other evidence I've cited, I think it is very troubling.
Given the importance of this decision and how deeply our beliefs about it can run, I do not necessarily expect that this single essay will immediately change someone's opinion. At the very least, I think readers will want to follow the links I've provided -almost all of them to primary sources- to see if my claims are correct. What, then, do I hope readers gain from what I've written?
First, I hope that this essay calls attention to claims that you may never have considered. In doing research on this subject, I learned quite a bit of new information, from both pro- and anti-vaccine sites, which I then had to incorporate into my beliefs about vaccines. For example, I first learned on an anti-vaccine website that the pertussis (whooping cough) vaccine has a relatively low effectiveness and that recent outbreaks of pertussis are probably not due to a drop in vaccination rates. This information was confirmed not only by anti-vaccine sites, but by pro-vaccine sites and multiple media sources. Given that I had assumed -incorrectly- that all vaccines were extremely effective, that new information required me to alter my belief. In the same way, if much of the material I presented in this essay is new to you, then it may be worth reevaluating your beliefs.
Second, the writing of this essay has made me realize how confusing the Internet can be, even to those who genuinely want to know the truth. As I've already said repeatedly, the best way to separate fact from fiction on the internet is to consult multiple sources with widely diverging viewpoints. Seek out both sides of the debate and weigh the evidence they present. Look for primary sources (interviews, legal documents, scientific studies). Even if you are not a scientist, the main conclusions of research articles are always summarized in the abstract, so try to read the article yourself rather than trusting a secondary source to tell you what the article says. Look for sites and sources which at least attempt to take an impartial tone and focus more on information than on accusation. That is not to say that clearly partisan sites cannot contain valid information, but rhetoric and emotion can often mask questionable interpretation of data.
Finally, I hope that this essay causes us to reflect on our own emotional commitment to certain beliefs and how hard it can be to change them. I suspect that parts of this essay made many people uncomfortable on both sides of this issue. For example, I'd imagine that some of the information regarding Dr. Wakefield's ethical practices and financial ties elicited an immediate, emotional response to people who view him positively. In the same way, I'd also imagine that some of the statements I made about the possibility of biased research or the possibility that anti-vaccine sites contain valid information elicited an immediate, emotional response to people who are strong proponents of vaccines. Like any normal human being, I experience these responses myself. We all have deep emotional investments in certain beliefs and when they are challenged, we can react with defensiveness and incredulity. But we have to fight against those emotional reactions and insist that our reason guide our emotions. Truth might be hard to find, unexpected, and even uncomfortable. But we need to remain open to it.
- Science and religion: is it either/or or both/and?
- Why should we believe that Christianity is true?
- Why I am a Christian
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.