Do Vaccines Cause Autism?

Paul A. Offit, MD, discusses the common concern related to vaccines and autism. He describes the origin of the hypothesis and subsequent scientific studies.


Do vaccines cause autism?

Paul Offit, MD: Hi, my name’s Paul Offit. I’m talking to you today from the Vaccine Education Center here at The Children’s Hospital of Philadelphia. Probably the question that’s most been entertained, I guess, regarding vaccines by the media, is the question about whether or not vaccines could cause autism. And this notion was born, really, in the late 1990s, associated with a publication of a paper in a British Journal called The Lancet, claiming that the combination measles, mumps, rubella, or MMR vaccine caused autism.

Now, that was … it raised the question. You can argue that what this paper did, it raised the question. You can argue it’s a reasonable question. I mean for some parents, “My child was fine. They got a vaccine, then a month, or two, or three later, they started to develop signs and symptoms of autism. Could the vaccine have done it?”

This is an answerable question. The way you answer it is you look at large numbers of children who either did or didn’t get the measles, mumps, rubella vaccine to see if you are at greater risk of having autism if you got the vaccine and if you didn’t. And there have been at least 12 studies now involving hundreds and hundreds of thousands of children on several continents that have found the exact same thing.

Most recently there was a study that was published in the Journal of the American Medical Association. It involved a database of 91,000 children. And what they did was they looked at younger children where the older child already had autism. To see whether … if that younger child got vaccinated or didn’t get vaccinated, whether the younger child, when vaccinated, was more likely to get autism. And an obviously an at-risk child because the older child, the sibling, already had autism. And the answer was no difference. Didn’t matter whether you vaccinated or didn’t vaccinate the younger child, there was an equal risk of getting autism.

So all you did by not giving that younger sibling vaccines was increase their risk of getting vaccine-preventable diseases without in any way decreasing their risk of getting autism.

Then what happened is the hypothesis, if you will, morphed to not that MMR vaccine caused autism, but that thimerosal, an ethylmercury-containing preservative in vaccines, caused autism. That was actually very easy to study. I mean, we had taken thimerosal out of vaccines in our country by the year 2000, at least as given to young child. There were Canadian provinces that used vaccines that contained thimerosal right next to provinces that used the same vaccines that didn’t contain thimerosal. Western Europe took thimerosal out of vaccines by 1991.

So, it was very easy to do the kinds of studies to see whether or not thimerosal had any impact on the development of autism. Or even subtle signs of mercury poisoning for that matter. And there was no association.

Then more recently this sort of the hypothesis morphed again. Do children just get too many vaccines to soon and that causes autism. Now, there’ve been a couple studies that have looked at that. Looking at children who got vaccines according to the recommended schedule, compared to those whose parents had chosen to delay, or withhold vaccines. And again, no difference in autism.

So I think while we don’t know what the cause or causes of autism is, I think what we can say with confidence is that vaccines aren’t it. It’s probably the best studied of the environmental factors associated with the … that people that have been concerned about regarding autism.


Related Centers and Programs: Vaccine Education Center

Last Reviewed on Aug 11, 2015