Sep 08 2008

Lack of Association between Measles Virus Vaccine and Autism

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A new study published in PLOS One shows no association between the MMR vaccine and autism or the presence of measles virus in the gut of children with autism and GI symptoms. This is yet more evidence against the claim that the MMR vaccine is responsible for some autism cases. Of course, no one study can clearly settle a complex medical question. The entire literature must be taken as a whole, and when we do this it becomes clear that the evidence is strongly against any association between MMR and autism. This new study is an important addition, and strengthens this conclusion.

This study has some interesting features. The lead author is Mady Hornig – who (until this study) was one of the research darlings of the anti-vaccine crowd. It will be difficult for the anti-vaccinationists to dismiss this study as coming from a vested interest or someone with an agenda, as they have previously be extolling the virtues of this particular researcher. Further, in the press release we learn:

(John Snow Professor of Epidemiology and director of the Mailman School’s Center for Infection and Immunity) adds, “The study design process was a critical piece for us, as there is still so much public concern over the safety of the MMR vaccine. For this reason, we involved the autism parent/advocacy community as we designed the study to ensure that all issues were being addressed. We are hopeful that this process of community engagement will build important partnerships among members of the autism community, physicians, public health agencies, and clinical researchers; serve as a paradigm for the conduct of future studies to understand the causes of this disorder; and facilitate the rapid communication of clinically relevant scientific findings to the broader community.”

I would love for this to be true. I applaud the approach – the scientific community reaching out to public groups, involving them in research design so that everyone can agree upon the results. This is what happens within the scientific community – both sides of a controversy come together and design a study that everyone can agree on. These are often referred to as consensus trials as they are meant to build consensus out of controversy. I have seen this work within my own field. Unfortunately, the anti-vaccinationists are ideologues not interested in the objective findings of science.

The study itself was a deliberate attempt to replicate the original study by Andrew Wakefield that sparked the entire MMR-autism scare in the first place. That Wakefield study has subsequently been refuted, specifically the lab he used to look for measles virus RNA in the guts of children with autism and GI symptoms was shown to be fatally flawed. The lab Wakefield used was run by professor O’Leary, and the process he used at the time by testimony left out key steps and therefore the results were worthless. Interestingly Hornig used O’Leary’s lab again, along with two other labs for confirmation.

The results showed that (from the abstract):

The objective of this case-control study was to determine whether children with GI disturbances and autism are more likely than children with GI disturbances alone to have MV RNA and/or inflammation in bowel tissues and if autism and/or GI episode onset relate temporally to receipt of MMR. The sample was an age-matched group of US children undergoing clinically-indicated ileocolonoscopy. Ileal and cecal tissues from 25 children with autism and GI disturbances and 13 children with GI disturbances alone (controls) were evaluated by real-time reverse transcription (RT)-PCR for presence of MV RNA in three laboratories blinded to diagnosis, including one wherein the original findings suggesting a link between MV and ASD were reported. The temporal order of onset of GI episodes and autism relative to timing of MMR administration was examined. We found no differences between case and control groups in the presence of MV RNA in ileum and cecum. Results were consistent across the three laboratory sites. GI symptom and autism onset were unrelated to MMR timing. Eighty-eight percent of ASD cases had behavioral regression.

So, there was no more incidence of having measles virus in the gut for children with and without autism, and there was no correlation in the timing of the MMR vaccine and the onset of GI symptoms or autism. As Hornig herself says, this removes the last bit of evidence put forth for an association between MMR and autism, by replicating the original Wakefield study and finding negative results. Therefore Wakefield’s claims have failed a critical component to the process of science – replication. And no one can reasonably claim bias in this case.

Sounds like a slam dunk against the MMR-autism link claim. Maybe the antivaccinationists will move on. Keep in mind that MMR has never had thimerosal in it and so this is a distinct claim from the one that thimerosal is linked to autism. When the MMR-autism link was going down in flames (even before this study) the anti-vaccine crowd moved onto thimerosal. Now that the thimerosal claim is scientifically dead they are moving on to “other toxins” in vaccines. This gets back to Dr. Snow’s wishful thinking above – the anti-vaccinationists will not be moved by this study. I still think such consensus trials are important, because it does further marginalize such fringe groups and the anti-vaccine movement, even though it does not touch the core of such movements.

Orac predicted a few days ago that the anti-vaccinationists would try to spin this study as support for the MMR hypothesis. He hinted at inside information, which has now been born out. Over at Age of Autism this is the spin:

However the study inadvertently gives credence to Wakefield and O’Leary’s previous work on measles virus and validates their earlier findings. It also substantiates the link between autistic regression and gastrointestinal disorder reported by Wakefield in his 1998 Lancet article.

The assumption is that because O’Leary’s results in this study were validated by two other labs, than his work 6 years ago must also have been legitimate.  This ignores the possibility that O’Leary cleaned up his lab’s act in response to the prior specific criticisms about procedure. I doubt Hornig would have used his lab if those deficiencies had not been corrected. AOA’s argument, therefore, is simply ludicrous.

The new study does suggest, however, that there may be an association between regressive autism and GI disorders (although not with the MMR or the measles virus). This requires further study and a common causality may be found.

The MMR-autism hypothesis was dead before this study was published, but this is yet more evidence against this notion. Yet the fears have been stoked, and the anti-vaccine ideologues continue their campaign to spread vaccine-preventable diseases.

The bigger picture here is the difference between how the scientific community behaves and how an ideological group behaves. Scientists are moved by the evidence, and will carefully examine questions just to be thorough – even beyond the practical need. They also (sometimes naively) live in a world where people are compelled by logic and evidence.  The anti-vaccinationists are not compelled by science or reason. They are starting with their conclusion and will embrace any evidence that supports it, no matter how dubious, and will dismiss any evidence that opposes it, no matter how solid.

Skeptics encounter this situation often. In this case, the anti-vaccinationists are causing direct demonstrable harm.

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