I know this is old news – or at least it should be – but it bears repeating, especially as we are in the midst of a resurgence of measles. There is no link between the mumps, measles, and rubella vaccine (MMR) and autism, or any neurological disorder. A new study confirms this lack of association. This should go a long way to reassure the vaccine hesitant that the MMR vaccine at least is safe and should not be avoided.

This is a Danish study, and the largest study of the MMR vaccine and autism to date – “657,461 children born in Denmark from 1999 through 31 December 2010, with follow-up from 1 year of age and through 31 August 2013.” They found:

During 5,025,754 person-years of follow-up, 6517 children were diagnosed with autism (incidence rate, 129.7 per 100,000 person-years). Comparing MMR-vaccinated with MMR-unvaccinated children yielded a fully adjusted autism hazard ratio of 0.93 (95% CI, 0.85 to 1.02). Similarly, no increased risk for autism after MMR vaccination was consistently observed in subgroups of children defined according to sibling history of autism, autism risk factors (based on a disease risk score) or other childhood vaccinations, or during specified time periods after vaccination.

Overall there was no association between getting the MMR vaccine and later being diagnosed with autism. Further, there was no correlation when looking specifically at children who have a sibling with autism, and therefore might constitute a susceptible subpopulation. Further still, there was no clustering of autism diagnosis following the MMR vaccine administration, as might be expected if there was a causal link. This is a very large study with an adequate study design, so that if there were any increased risk of developing autism from the MMR vaccine we should be seeing it in this data – and we don’t.

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Part of the impetus for the fringe belief that vaccines are somehow causally related to the development of autism is that the signs of autism often become apparent at 2-3 years of age, after children have received many of their routine childhood vaccinations. (Average age at diagnosis is 3.1 years.) In an otherwise healthy child, the vaccines might be the only thing the parents can think of that could be a potential cause.

Signs of autism are not clinically noticeable prior to 6 months of age. From about 6-18 months the signs can be detected by careful clinical observation, but may be missed by parents. During this time parents may become slowly aware that their child is not developing as expected, and the creeping suspicion that something is not quite right often culminates in a diagnosis between age 2-3.

The phenomenon of temporal binding may then cause the parent’s memories to shift over time so that the temporal correlation between getting vaccines and signs of autism appearing become closer together. For some parents this can become a very powerful memory – my child was perfectly normal, then he received vaccines and started to show signs of autism.

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We can add one more study to the pile of evidence showing no association between exposure to thimerosal (a mercury-based vaccine preservative) and autism. The article: Prenatal and Infant Exposure to Thimerosal From Vaccines and Immunoglobulins and Risk of Autism, is published in the latest issue of Pediatrics, and shows no association between prenatal and infant exposure to thimerosal and three forms of autism – autism, autism spectrum disorder, and regressive autism.

No one study can ever be definitive, but now we have a large body of evidence from multiple studies showing a lack of association between thimerosal and autism. This won’t stop the dedicated anti-vaccinationists and mercury militia from continuing their anti-vaccine propaganda, but hopefully it will further reassure those who actually care about the science.

Background

This has been a long and complex story, so let me review some of the background. Diagnosis rates of ASD have been climbing for the last 20 years, prompting some to search for an environmental cause. The existing anti-vaccine community, not surprisingly, blamed vaccines. This was given a tremendous boost by the now-discredited study by Andrew Wakefield concerning MMR (which never contained thimerosal) and autism. When the evidence was going against MMR as a cause, attention turned to thimerosal in some vaccines. This notion was popularized by journalist David Kirby in his book, Evidence of Harm.

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I love a good sequel. Aliens, of course, was the best sequel ever – that rare event when the sequel is actually better than the original movie (of course, the series went down hill from there, like Star Trek it peaked with the second movie).

Last year we heard the results of the Autism Omnibus – a special court with three special masters set up to resolve about 5,000 cases before the vaccine court claiming that autism resulted from vaccines – either the MMR vaccine or thimerosal (a mercury-based preservative in some vaccines, but removed from most by 2002). In the US there is a Vaccine Injury Compensation Program (VICP) which bypasses the regular courts and awards compensation to those injured by vaccines, paid for by a small tax on each dose of vaccine given. The purpose is to rapidly compensate those who might have been injured (the threshold for evidence is quite low) and to encourage pharmaceutical companies to manufacture vaccines (the threat of suit would make it not viable otherwise).

Over 2008 the Autism Omnibus heard three cases that were presented as the test cases (presumably the best cases they could come up with) for the theory that the  MMR vaccine (with or without thimerosal from other vaccines – MMR never had thimerosal) caused or contributed to autism in some individuals. They ruled against all three cases, stating in very strong terms that there is no evidence to back up the claims of a link between MMR and autism. Judge Hasting wrote of one case – Cedillo:

Considering all of the evidence, I found that the petitioners have failed to demonstrate that thimerosal-containing vaccines can contribute to causing immune dysfunction, or that the MMR vaccine can contribute to causing either autism or gastrointestinal dysfunction. I further conclude that while Michelle Cedillo has tragically suffered from autism and other severe conditions, the petitioners have also failed to demonstrate that her vaccinations played any role at all in causing those problems.

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This week on Science-Based Medicine I wrote an article about a new study looking at the onset of autism symptoms, showing that most children who will later be diagnosed with autism will show clear signs of autism at 12 months of age, but not 6 months. This is an interesting study that sheds light on the natural course of autism. I also discussed the implications of this study for the claim that autism is caused by vaccines.

Unfortunately, I made a statement that is simply wrong. I wrote:

Many children are diagnosed between the age of 2 and 3, during the height of the childhood vaccine schedule.

First, this was a vague statement – not quantitative, and was sloppily written, giving a different impression from the one I intended. I make these kinds of errors from time to time – that is one of the perils of daily blogging about technical topics, and posting blogs without editorial or peer-review. Most blog readers understand this, and typically I will simply clarify my prose or correct mistakes when they are pointed out.

However, since I often write about topics that interest dedicated ideologues who seek to sow anti-science and confusion, sometimes these errors open the door for the flame warriors. That is what happened in this case.

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Like my science-blogging colleagues, I get e-mail. I always appreciate it when readers (or listeners, in the case of the SGU) take the time to write. Sometimes the e-mails are questions from someone who disagrees with my position on a hot issue. I especially like these e-mails – they are good blog fodder, and I think the format of answering questions is more compelling and interesting than making a didactic argument.

Below is an example of the kind of question I most like to get – from someone who disagrees with me, but still manages to ask polite and cogent questions. This stands in stark contract to most hostile e-mail I get, which are just strings of ad hominems, straw men, and other logical fallacies. I get the impression (and some of my e-mailers have later even admitted this) that the e-mails were not meant as an opening to serious discussion, but as a venting rant into the ether of the internet.

Harold asks some very important questions about the alleged autism-vaccine link and research priorities, and I am happy for the opportunity to clarify my position. His e-mail begins below the fold:
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Politics is partly about setting priorities and agendas, and therefore it is impossible to keep politics out of science. Politicians are also in control of the public’s purse strings, and so funding science also cannot be free from politics.

But ideally we should have an atmosphere in which politicians and funding agencies set broad agendas, and then let scientists decide the details of which research should be funded based upon the science. It is, in fact, an important trust that public money that is spent on scientific research be utilized optimally, and not to promote someone’s narrow ideological agenda. Examples of abuses are legion; my favorite example is the National Center for Complementary and Alternative Medicine (NCCAM), Senator Tom Harkin’s pet project in which the usual standards of medical research have been subverted to promote sectarian medicine.

We want scientists to follow their noses – to research those questions they think are most fruitful. But scientists are often forced to follow the funding, and this distorts the direction of research. Industry funding distorts research in ways that are advantageous to industry – a real problem that is being examined and there are at least attempts to deal with it. Government funding should be neutral, and provide a counterbalance to industry funding, but is often subverted to ideology. Even well-meaning patient-groups can distort funding if they try to dictate what scientists should be researching in exchange for their fund-raising, with detrimental effects.

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The anti-vaccine community is tireless. As I wrote yesterday, they happily shift around their multiple goalposts as long as they have some working hypothesis about how vaccines are to blame for autism or some human suffering. They have moved from MMR to thimerosal to aluminum to “toxins” to squalene and now the HepB vaccine. They just spin the wheel and choose their next target – although they never really abandon their prior targets, they just back burner them a bit.

They also have their small dedicated group of researchers, like the father and son team of Geier and Geier, to produce crappy studies to support their anti-vaccine claims. Andrew Wakefield, who has been rightly vilified for starting the MMR scare with his now discredited Lancet study, has also apparently decided to make a career out of feeding bad studies to the anti-vaccinationists.

I acknowledge there is a certain symmetry to the situation now. The scientific community presents studies that show a lack of correlation between some aspect of vaccines and autism or other neurological disorders. They generally accept these studies as supporting vaccine safety, even while being open about their limitations. They also sharply criticize those studies that suggest there may be a connection between vaccines and autism as fatally flawed.

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Two recent studies concerning the prevalence of autism in the US have been getting a lot of attention, because they indicate that autism prevalence may be higher than previously estimated. This, of course, fuels the debate over whether or not there are environmental triggers of autism.

One study was conducted by the CDC but has yet to be published. The results were announced ahead of publication by the US Health and Human Services Secretary Kathleen Sebelius to the autism community. She reports that the new prevalence of autism spectrum disorder (ASD) is now estimated at 1% or 100 in 10,000 children. This is an increase over the last few years. In 2002 the prevalence was estimated to be 66 per 10,000.

The second study was published in the journal Pediatrics and is a phone survey of 78,037 parents. They asked if they had any children who had ever been diagnosed with an ASD. Here are the results:

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The much awaited decision on the first test case of the Autism Omnibus was just announced – and it’s good news. They have found that the petitioners failed to make their case that vaccines caused their children’s autism, and that therefore compensation was not appropriate.

The Autism Omnibus hearings were set up to evaluate for thousands of petitions for compensation under the vaccine injury compensation program. This is a program set up in the US to compensate those who suffer adverse effects from vaccines, and it is paid for by a tax on all vaccines. This is a sensible system because it allows manufacturers to produce much needed vaccines without risking bankruptcy over fad pseudoscientific accusations – like those that took down Dow Chemical. It also more quickly and fairly compensated families, which is fair given that vaccines are somewhat compulsory in the US (although in most states it is all too easy to get an exemption).

These cases arise out of the now scientifically discredited notion that certain vaccines or something in vaccines (like thimerosal) is linked to autism. I have written extensively about this controversy, and what we can say at this time is that the scientific evidence is solidly against any link.

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