For a long time I thought there would be no need for me to write about the misconception that vaccines would somehow be connected to autism. This is a point that has been so extensively studied that there is no way the myth could persist. Right? Well, after several requests to include this topic, and coming across online discussion forums referring people to my articles where many still vigorously subscribe to this idea, I decided it was time. If you are in a hurry, here is a graphic summary of some of the main conclusions from the research:

How did people get the idea in the first place?

This story has been told many times. One excellent recollection of the events can even be read in a form of a cartoon The Facts In The Case Of Dr. Andrew Wakefield. Long story short: one study in 1998 claimed a connection between autism and the measles, mumps, and rubella (MMR) vaccine, but the author of the study, Andrew Wakefield, turned out to have been financed by the lawyer who hoped to produce evidence to use in court. Meanwhile, Wakefield had also filed patents for a single measles vaccine, which he hoped would be given in the place of the combination MMR vaccine. Conflict of interest was great indeed, and in this case it also turned out that the data in the study was falsified. All other authors retracted their names, and the study was withdrawn. You can read how the case against the MMR vaccine was fixed in the British Medical Journal.

Wakefield lost his medical licence. He by no means has stopped campaigning for the connection which he failed to find evidence for. Recently Wakefield gave talks in the US on a ConspiraSea Cruise, among speakers on topics such as astrology, crop circles, tax fraud, dowsing, HAARP, mind control, and even the idea that death itself is a conspiracy. Wakefield campaigns his image as one of a victim in possession of hidden truths.

Yes, this really is it. Since autism is often not confirmed or properly detected until after the first year of life, parents easily grab hold of different things that happen around then to find something to blame, even if the actual changes leading to autism development have occurred even before birth (more on that soon). There has never been any other evidence to go on. After this falsified study, however, during the last decade and a half, more than 14 million children have been included in a wide array of autism studies, and their conclusions are clear: no connection between vaccination and the development of autism can be found.

The MMR vaccine does not cause autism

The Healthcare Triage has made an excellent short video summary of all the studies looking at vaccines and autism. Here’s the page on The Incidental Economist which lists the resources presented in writing as well. The Logic of Science has also provided a thorough review of the evidence on the topic of vaccines and autism if you are interested in reading about circa 160 or so papers in detail (yes, I meant thorough). I will go through the main conclusions from these studies.

There have been two Cochrane reviews looking at this topic, for instance, the latest including studies looking at 14.7 million children in total, and they state the following:

Exposure to the MMR vaccine was unlikely to be associated with autism, asthma, leukaemia, hay fever, type 1 diabetes, gait disturbance, Crohn’s disease, demyelinating diseases, bacterial or viral infections.

To note some of the larger individual studies, there is one Finnish and one Danish study looking at more than half a million children each, and, you guessed it, both show no link between measles, mumps, and rubella (MMR) vaccination and autism.

Another striking case in point is a study looking at 300,000 children in Japan: the incidence of autism increased during several years while their MMR vaccination rate fell markedly (1988-1992) and incidence continued to rise even more during a time when no MMR was administered at all (1993-1996). The study conclusion:

The significance of this finding is that MMR vaccination is most unlikely to be a main cause of ASD, that it cannot explain the rise over time in the incidence of ASD, and that withdrawal of MMR in countries where it is still being used cannot be expected to lead to a reduction in the incidence of ASD.

There has also been research looking not at MMR vaccination specifically, but at exposure to any vaccine antigens, and again, finding no link between the amount of antigens the child receives, and the development of autism: Increasing Exposure to Antibody-Stimulating Proteins and Polysaccharides in Vaccines Is Not Associated with Risk of Autism.

There has even been a study funded by an anti-vaccine autism group where they hope to confirm a preliminary inclination of some measurable difference in monkey babies’ development after vaccines, as reported by Newsweek: “Anti-vaxxers accidentally fund a study showing no link between autism and vaccines”. The group behind the funding seems unhappy with the results of the study: Administration of thimerosal-containing vaccines to infant rhesus macaques does not result in autism-like behavior or neuropathology. To end with yet another review, Immunizations and autism: a review of the literature states the following:

Our literature review found very few studies supporting this theory, with the overwhelming majority showing no causal association between the Measles-Mumps-Rubella vaccine and autism. The vaccine preservative thimerosal has alternatively been hypothesized to have a possible causal role in autism. Again, no convincing evidence was found to support this claim, nor for the use of chelation therapy in autism.

Which brings us to the second-most commonly suggested culprit: mercury.

Thimerosal does not cause autism

Some have argued that it was not the vaccines per se, but the mercury in these vaccines, that might cause autism, pointing to thimerosal (aka thiomersal), which is a vaccine preservative containing mercury. Many people fear mercury because of the commonly known poisonous properties of methylmercury. This, however, is not the form found in thimerosal: when it dissociates it releases ethylmercury. Due to a purely precautionary fear, thimerosal was removed from childhood vaccines in 2002. What about autism incidence? You guessed it, no change. You can read more about thimerosal, and the difference between methyl and ethylmercury in my piece Mercury in retrogade.

Please see the piece Mercury in retrogade for sources. Note – a methyl group per se is not a problematic element (or more problematic than an ethyl group). The effects of a compound always depend on the molecular context. Methylation of DNA and proteins are part of normal cell regulation, for instance.

Many scared parents still continue to blame thimerosal for autism, although no connection has been found after extensive research, and the autism incidence has not decreased after removal of thimerosal. See several studies below refuting any connection of autism to the thimerosal in vaccines:

• “Association between thimerosal-containing vaccine and autism. Conclusion: The results do not support a causal relationship between childhood vaccination with thimerosal-containing vaccines and development of autistic-spectrum disorders.”

• “Continuing increases in autism reported to California’s developmental services system: mercury in retrograde.”

• “Thimerosal exposure in infants and developmental disorders: a retrospective cohort study in the United kingdom does not support a causal association.”

Science based medicine has also written about the lack of effect on the rates of autism incidence, seeing as people who campaigned for thimerosal’s removal predicted that it would result in a significant decrease, but…

…rates have continued to rise without even the slightest change in the rate of increase. This is a powerful refutation of the thimerosal-autism hypothesis, and has been replicated in other countries.

What does cause autism? Is autism incidence rising?

Signs of autism can actually be identified much earlier than the MMR vaccine is given, according to a paper published in Nature in 2013, where they report that infants that will later be diagnosed with the disorder begin to avoid eye contact at two months of age. This in itself already hints at the conclusion drawn from the research so far, namely, that autism is genetic. It is a very heterogenous disorder, what comes both to the degree of disorder and to the number of possible genes involved. Nature News reports on autism’s genetic background as follows:

…results indicate that spontaneous duplications or deletions of at least 130 sites in the genome could contribute to the risk of autism. Wigler believes that in total there are closer to 400 such sites. “It is a large number,” he acknowledges, and that will make it harder to develop therapies that will benefit a large fraction of patients. “Given the number of genes that might cause autism, one shouldn’t expect that one treatment is going to cure them all,” says Wigler.

Considering the amount of purported autism ‘cures’ sold, mostly without any basis in evidence, often risking significant harm to autistic children, that last line is an important one to keep in mind.

A study published in 2012 reports positive results from blood tests screening for a pattern of gene expression that can help identify 80-85 % of babies with autism at 12 months old, also covered in the Australian ABC news. Yet newer research finds changes in the brains of most autistic children which have occurred long before birth, as reported in BBC.

Another review of autism from 2013 reaches a similar conclusion concerning the causes of the disorder:

In this article, we review the history of the identification and classification of autism and the origin of the now widely-debunked autism/vaccine hypothesis. […] Finally, the evidence that autism is fundamentally a genetic disease is discussed, including family studies, the role of DNA copy number variation and known single gene mutations.

If you would like to read more about autism research, one good site to continue on is Autism Science Foundation. It is important to mention that it has been questioned whether a real rise in the incidence of autism even exists, or if the apparent increase does not mostly result from better recognition and awareness of the disorder. Science based medicine argues that this is the best supported conclusion:

Further, the best epidemiological evidence suggests that the rise in the diagnosis rate of ASD is an artifact of broadening the definition of autism, diagnostic substitution, and increased surveillance. Therefore there isn’t really an autism “epidemic” just a change in the definition and efforts to make the diagnosis.

Why do people still claim there is a connection?

Many people continue to spread the claim that vaccines cause autism. For distressed parents it may be important to find a culprit, and others may make a profit from selling a supposed cure based on removal of the purported cause. Some people find comfort in holding fast to the belief in a conspiracy, thinking that the government (all governments?) must be hiding the information. See for instance the “CDC whistleblower” scandal, where quotes were taken out of context and a small sub-population of a study was lifted out of the context of its clear confounding factors, covered well by Left Brain Right Brain, Science-Based Medicine, and Respectful Insolence, discussed more also in the comments-section of this piece.

Image from Refutations to Anti-Vaccine Memes

As an example of continued autism-claims, you can read a post on a blog on learning disabilities and parenting called I Speak Of Dreams – they have taken a look at an anti-vaccine document with over 70 papers that allegedly prove a connection between autism and vaccines. This tactic is an attempt to overwhelm the reader by the sheer number of links and citations, to convince someone with what appears to be big pile of evidence.

Update: this list, still often used by anti-vaccine proponents, has grown to include 124 papers, each and every one of which has been addressed in a very long and detailed blog post by a surgeon, blogging as DocBastard, here.

When you sit down and look at the articles in this list, you find one by one, that they a) don’t actually relate to the topic; or b) aren’t research but opinion pieces; or c) don’t actually conclude that which you were led to believe; or d) have vital methodological flaws; and e) have not been confirmed by further research.

I will give an example from this list that exemplifies quite a few of the points above and demonstrates the misunderstanding around mercury. In this study from 1994, presented to the reader in this context as evidence for vaccine-autism link, the researchers looked at reactive glial cells in the visual cortex of monkeys. They were looking at primate brains – that at least could be relevant as a piece of the puzzle for a body of research looking at what the effects could be on humans. But the type of mercury exposure they studied? It was methylmercury – the kind found in fish but not in vaccines.

Not only that, but the monkeys were exposed to very high doses: 50 micrograms methylmercury per kilogram body weight per day, for months. The equivalent of which would be a 30 kg (66 lbs) monkey eating 30 cans of tuna per day. Anyone arguing for a connection between vaccines and autism should lose all credibility after putting this kind of study forward as relevant evidence.

Why? Because, methylmercury bioaccumulates, ethylmercury does not. You can read more about it in my piece Mercury in retrogade. Suffice it to say that methylmercury is known for its poisonous effects and would never be used in vaccines. It’s important to understand that different substances can have very different effects in the body.

The way to evaluate a complex health topic is to look at the bestscientific evidence available (Why science? – read more about what sets science apart). That means review articles, at first hand, and large, well designed studies of humans should be given more weight than small pilot studies, or studies in laboratory animals. In this case, they all come to an astoundingly clear conclusion: autism is not connected to vaccines in any way. Autism is a very complex topic, and many parents find themselves hoping to find a simple explanation. But sometimes life just doesn’t work that way. Sometimes it’s complex.

If you hear something that sounds scary about vaccines, you should try to learn more about it from legitimate sources such as the World Health Organisation or other science and health care institutions. The natural world is nuanced and looking at it properly takes a lot of time and care.

If you’d like to read more about vaccine topics, please check out my page Vaccines and health.

If you would like to ask a question or have a discussion in the comments below, you are very welcome, but please take note of my Commenting policy. In a nutshell: