MMR vaccine (still) doesn't cause autism, new study finds

Nope.

We’re still spending vast amounts of time and money trying to counter the ill effects of a discredited, retracted paper from 1998 that claimed to find a link between the MMR (measles, mumps, and rubella) vaccine and autism. Even after the The Lancet retracted the study, and even after the British Medical Council revoked the medical license of its lead author, Andrew Wakefield, many people continue to withhold vaccines from their children because of a fear that somehow, despite all the evidence to the contrary, vaccines might cause autism. Vaccines, I hasten to add, have saved millions of lives and are probably the greatest medical advance of the past two centuries.

Now another study has appeared to add more weight to the evidence about the safely of the MMR vaccine. The new study by Anjali Jain and colleagues, just published in the Journal of the American Medical Association, looked at a huge number of children–95,727–for evidence of any link between autism and the MMR vaccine.

The results were not surprising, to those who have been following the science. To quote the conclusions directly: 

“Receipt of the MMR vaccine was not associated with increased risk of ASD [autism spectrum disorder], regardless of whether older siblings had ASD. These findings indicate no harmful association between MMR vaccine receipt and ASD even among children already at higher risk for ASD.”

That should settle it, right? But then, dozens of previous studies should have already settled this question. Unfortunately, due to the ongoing activism of anti-vaccine groups such as Age of Autism, (who already attacked this new study) and to conspiracy theorists such as Robert F. Kennedy Jr. (whom I wrote about last summer, and who was campaigning against vaccines in Vermont just last week), misguided claims that vaccines cause autism or neurological problems persist.

Here are the numbers from the new study. The authors compared vaccinated children to unvaccinated children, using a huge database of medical claims that included at least 5 years of followup. (This was an "observational" study, by necessity–it would be unethical to withhold vaccines from children on purpose.) The relative risk for autism in children who had 2 doses of the MMR vaccine (the recommended amount) compared to unvaccinated children was 0.74. In other words, a child was somewhat less likely to be diagnosed with autism if he or she were vaccinated. 

Even more surprising was the relative risk among children who had an older sibling with autism: in this smaller group, children with 2 doses of MMR were just 44% as likely to be diagnosed with autism as unvaccinated children. This statistically significant finding indicates, unexpectedly, that vaccines might actually protect children from autism.

The authors were quick to note that there are other good reasons for this apparent protective effect of vaccines: in particular, if parents of autistic children withheld vaccines from their younger children, this could explain the effect. Why? Because we know that autism has a genetic component, and that if one child has autism, his younger sibling is more likely (because they share many genes) to have autism as well. Jain and colleagues explained that if these parents withheld vaccines–because of fears spread by the anti-vaccine movement–then their children could contribute to the apparently lower rate of autism in children who were vaccinated. The authors couldn’t rule out a protective effect of vaccines, but scientifically it seems unlikely, and they wisely offered an alternative explanation.

So: once again we have a large, carefully conducted study showing that the MMR vaccine does not cause autism, and even finding evidence that vaccinated children have lower rates of autism. Let's hope this study helps to end the anti-vax movement, so that we can soon stop spending time and money trying to refute their long-discredited hypotheses and instead focus on trying to understand the true cause.