One more bit of evidence burying the ex-hypothesis that vaccines cause autism

May I just say something again? (Actually, it’s my blog; so I’ll say it if I want to regardless of whether you want me to or not.) You know that “hypothesis” that vaccines cause autism, the one that has been at the core of the modern antivaccine movement over the last 15 years or so? Well, it’s not pining for the fjords, if you know what I mean. No it’s not pinin’! It’s passed on! This “hypothesis” is no more! It has ceased to be! It’s expired and gone to meet it’s maker! (Well, actually, since one of its makers, Andrew Wakefield, is still around, I’m not sure what in practice that actually means.) It’s a stiff! Bereft of life, it rests in peace! If antivaccinationists hadn’t nailed it to the perch it’d be pushing up the daisies! Its metabolic processes are now ‘istory! It’s off the twig! It’s kicked the bucket, It’s shuffled off this mortal coil, run down the curtain and joined the bleedin’ choir invisible!! THIS IS AN EX-HYPOTHESIS!!

Sorry, but I just have to do that every so often because I like both Monty Python and rhetorically beating on antivaccinationists, and I just had a nice excuse to indulge my passion for both.

Actually, this bit of fun was delayed because there was a problem over the weekend. Sometimes it’s a good problem to have; sometimes not so good. As it turned out, there were just too many things out there that I wanted to blog about. So I picked and I chose, and ended up writing about Mike Adams’ ham-fisted attempt to use legal thuggery to silence a critic, as well as another topic at my not-so-super-secret other blog. Now that that satisfying bit of blogging is taken care of, it’s time for what will be another satisfying bit of blogging. I’m referring to a large meta-analysis that demonstrates once again something that regular readers of this blog already know. Specifically, it comes to the not-unexpected conclusion that vaccines are not associated with autism. In fact, that’s the title of the meta-analysis by Taylor et al, Vaccines are not associated with autism: An evidence-based meta-analysis of case-control and cohort studies. It’s an article in press, but can be found here.

Let’s take a step back. The results of this study are singularly unsurprising. The reason is, well, because it’s a meta-analysis. As I’ve discussed time and time again, the overwhelming preponderance of evidence does not support the now discredited idea that there is a correlation between vaccines and autism (or, for that matter, between the mercury-containing preservative thimerosal that used to be in childhood vaccines). Taken in its totality, the evidence is most consistent with the conclusion that there is no association between vaccines and autism, so much so that if there is a correlation it would have to be incredibly small to be less than the expected noise inherent in large epidemiological studies.

I’m going to cut to the chase (I know, I know, uncharacteristic of me) and list the findings first. Then I’ll discuss a bit about the methods:

Five cohort studies involving 1,256,407 children, and five case-control studies involving 9,920 children were included in this analysis. The cohort data revealed no relationship between vaccination and autism (OR: 0.99; 95% CI: 0.92 to 1.06) or ASD (OR: 0.91; 95% CI: 0.68 to 1.20), or MMR (OR: 0.84; 95% CI: 0.70 to 1.01), or thimerosal (OR: 1.00; 95% CI: 0.77 to 1.31), or mercury (Hg) (OR: 1.00; 95% CI: 0.93 to 1.07). Similarly the case-control data found no evidence for increased risk of developing autism or ASD following MMR, Hg, or thimerosal exposure when grouped by condition (OR: 0.90, 95% CI: 0.83 to 0.98; p = 0.02) or grouped by exposure type (OR: 0.85, 95% CI: 0.76 to 0.95; p = 0.01). Findings of this meta-analysis suggest that vaccinations are not associated with the development of autism or autism spectrum disorder. Furthermore, the components of the vaccines (thimerosal or mercury) or multiple vaccines (MMR) are not associated with the development of autism or autism spectrum disorder.

In other words, in a group of studies that encompass nearly 1.3 million children, there was no hint of an association between vaccination and autism or between vaccination and autism spectrum disorder (ASD) and no relationship between mercury exposure in vaccines through thimerosal-containing vaccines and autism or ASD. Perhaps most shocking to me, the authors assert (and I have no reason to doubt) that this is the first quantitative pooling of data in a meta-analysis to look at the question of whether there is a correlation between vaccines and autism. This is an omission in the medical literature that is hard to believe.

The authors note that there have been twelve systematic reviews of the literature covering the relationship between vaccines and autism and that only one of them concluded that there was a correlation between the two. Can you guess who wrote it? Yes, it was that infamous turd of a review by Helen V. Ratajczak published in 2011 and trumpeted far and wide by the antivaccine movement. Let’s just put it this way. I was rather shocked that the authors even bothered to include this massive bit of antivaccine pseudoscience. Remember, this was the paper in which Ratajczak claimed that human DNA from vaccines was taken up in human brain cells in a form that could produce foreign proteins and provoke autoimmunity. I kid you not. When that article came out I couldn’t resist producing one of my characteristically logorrheic deconstructions that demonstrated exactly why her article was a proverbial steaming pile of fetid dingo’s kidneys. I suppose the authors had to mention her article, but it’s so full of pseudoscience, misrepresentation of science, and twisting of evidence that a good case could be made for not including it and saying that eleven out of eleven systematic reviews conclude that there is no relationship between vaccination and autism.

Of course, a meta-analysis is not a new study. It’s a study that aggregates existing studies, and, as I’ve often said, the danger of meta-analysis is what I like to call the “garbage in garbage out” phenomenon. In other words, aggregating a bunch of bad studies won’t magically turn them into gold, like some alchemist. So what about the studies included? Fortunately, they’re all decent studies, basically the big names that get cited time and time again, studies such as Price et al (for example). They also excluded studies that used the Vaccine Adverse Events Reporting System (VAERS) as their data source as described:

Papers that recruited their cohort of participants solely from the Vaccine Adverse Event Reporting System (VAERS) in the United States were not included due to its many limitations and high risk of bias including unverified reports, underreporting, inconsistent data quality, absence of an unvaccinated control group and many reports being filed in connection with litigation [5] and [6].


Not surprisingly, antivaccinationists are not pleased with the publication of this particular meta-analysis. Even though it’s not the be-all and end-all of evidence with respect to vaccines and autism, it is yet another piece of evidence demonstrating that vaccines are not correlated with autism. True, it’s a particularly powerful piece of evidence, but just a piece nonetheless. I’m also enormously puzzled why the editors of Vaccine allowed the authors to publish this “epilogue” from Guy Eslick, the senior author:

As an epidemiologist I believe the data that is presented in this meta-analysis. However, as a parent of three children I have some understanding of the fears associated with reactions and effects of vaccines. My first two children have had febrile seizures after routine vaccinations, one of them a serious event. These events did not stop me from vaccinating my third child, however, I did take some proactive measures to reduce the risk of similar adverse effects. I vaccinated my child in the morning so that we were aware if any early adverse reaction during the day and I also gave my child a dose of paracetamol 30 min before the vaccination was given to reduce any fever that might develop after the injection. As a parent I know my children better than anyone and I equate their seizures to the effects of the vaccination by increasing their body temperature. For parents who do notice a significant change in their child’s cognitive function and behaviour after a vaccination I encourage you to report these events immediately to your family physician and to the ‘Vaccine Adverse Event Reporting System’.

To be honest, I don’t recall ever seeing anything like this in a scientific paper before, and including such commentary in the paper itself is unscientific and unnecessary. I realize that the authors probably wanted to demonstrate that they understand parental fears, but I would submit that the discussion of a scientific article reporting peer-reviewed results of a meta-analysis of the literature examining the question of whether vaccination can cause autism. Such an anecdote might be appropriate in an accompanying editorial or in a commentary, but it’s completely inappropriate for an actual scientific studie or meta-analysis.

That curious misstep aside, this appears to be a well-designed meta-analysis. One could argue that it’s unnecessary because it doesn’t tell us anything we don’t already know, but doing meta-analyses instead of systematic reviews seems to be more in fashion these days; so I’m content to go with it. Not that it will ever persuade antivaccinationists that vaccines are safe and effective, but it’s useful as another bit of dirt to put on the grave of the ex-hypothesis that vaccines cause autism.