Thursday, 4 November 2010

The Anti-Vax Nexus: Autism & Vaccines

The Anti-Vax Nexus: Autism and Vaccines


As you will recall, yesterday I linked to and analyzed a post on the website Age of Autism, which is ostensibly dedicated to advocacy for children and adults on the autism spectrum and their families.

However, once you review enough past posts, it appears that Age of Autism is not really interested in undertaking positive action to research the etiology of autism spectrum disorders or to promote more-or-less proven therapies to assist people on the spectrum operate in the "hostile environment" (so to speak) of modern society.

Instead, the management of Age of Autism have adopted the position that vaccines are to blame for autism spectrum disorders (that is, that autism is an adverse effect of vaccination) and the scale of modern mass vaccination is responsible for present autism prevalence. It so happens that AoA is not alone in this regard. Indeed, the interrelation of vaccines and autism lies at the heart of the contemporary anti-vaccine movement - it is what I will call here the Anti-Vax Nexus.


The Core Claim of the Nexus


The observations that underly the core claim of the vaccine-autism connection are three-fold:
  1. That there has been a recent increase in the prevalence of autism spectrum disorders.
  2. That this increase has tended to track an increase in the use of mass vaccinations.
  3. That parents have reported their children to be expressing behaviours characteristic of autism spectrum disorders - to the point where they are diagnosed as being on the spectrum - after receiving vaccinations.

The inference follows quite naturally from these three observations: Vaccines cause autism. This is the core claim of the Nexus.

To be sure, not all anti-vaccine or vaccine-autism activists make this core claim quite as baldly or as unreservedly. More commonly, you will hear that specific ingredients in vaccines (most often thimerosal) are the causal factors, or that specific vaccines (most often the measles-mumps-rubella - MMR - vaccine) are the ones that cause autism. The core claim, however, remains intact in all these variants: vaccines, by virtue of one or more of their properties, cause autism.

Premise 1: Autism Prevalence
The below graph, from Wikipedia, shows the apparent increase in autism diagnoses in the United States from 1996 to 2007:

Apparent increase in autism prevalence, 1996-2007, United States. The rate increases approximately 6-fold in this period, prompting concerns of an epidemic.

Looks pretty ominous, doesn't it?

However, when epidemiologists got on the case, they found the picture wasn't quite as unequivocal. For example, this paper (Shattuck P 2006).

I would like to draw to your attention to three quotes from the paper:

RESULTS. The average administrative prevalence of autism among children increased from 0.6 to 3.1 per 1000 from 1994 to 2003. By 2003, only 17 states had a special education prevalence of autism that was within the range of recent epidemiological estimates. During the same period, the prevalence of mental retardation and learning disabilities declined by 2.8 and 8.3 per 1000, respectively. Higher autism prevalence was significantly associated with corresponding declines in the prevalence of mental retardation and learning disabilities. The declining prevalence of mental retardation and learning disabilities from 1994 to 2003 represented a significant downward deflection in their preexisting trajectories of prevalence from 1984 to 1993. California was one of a handful of states that did not clearly follow this pattern. [From the abstract.]

and

[T]he administrative prevalence of autism, as of 2003, in the majority of states was below what we would expect based on recent epidemiological estimates of the prevalence of autism among children ages 3 to 10 in the United States, which ranged from 3.4 to 6.8.32,33 The mean administrative prevalence of autism in US special education among children ages 6 to 11 in 1994 was only 0.6 per 1000, less than one-fifth of the lowest CDC estimate from Atlanta (based on surveillance data from 1996). Therefore, special education counts of children with autism in the early 1990s were dramatic underestimates of population prevalence and really had nowhere to go but up. [Discussions, second paragraph of the section.]

and

Environmental explanations for growing autism prevalence have been advanced in recent years, especially the potential role of vaccines. The majority of recent studies have failed to establish a connection between measles-mumps-rubella vaccination or the use of mercury-based vaccine preservative and autism.20,44–48 However, continuing inquiry into these posited links may yet reveal a connection between environmental exposure and consequent onset of autism. The present findings that support the plausibility of the role of changing identification practices being associated with increases in administrative prevalence should not be taken as a refutation of potential environmental explanations because growing administrative prevalence could very well have multiple causes including diagnostic substitution and environmental factors. [Discussion section, eighth paragraph.]

The paper does not, I should point out, rule out environmental factors as contributing to an increase in autism prevalence. It merely concludes that at least some of the apparent increase in autism diagnoses was a result of diagnostic substitution - and indeed, as noted in the second quote above, epidemiological estimates of autism prevalence were at one point higher than administrative reports of prevalence, so it may be no surprise that the apparent prevalence eventually increased.

Premise 2: Population-Level Correlation with Vaccination
The second premise notes a correlation: during the period in which autism prevalence increased (however real the increase), so did the vaccine schedule. Here is the current recommended vaccine schedule for Canada and (for children from birth to 6 years) for the United States. As you can see, that is a lot of shots, and a not-quite-anti-vaccination position exists which suggests parents should use various alternative schedules, delaying or doing without certain vaccines, if they find this schedule too intimidating. Usually, the basis for this premise has to do with the amount of antigens that infants and children are presented with by getting vaccinated.

However, as this paper documents, the antigenic load in the US pediatric schedule is actually very low (text summary on page 7, table on page 8). Once again, over to Dr Mark Crislip, this time with The Infection Schedule vs. The Vaccine Schedule, which provides the differing antigenic loads from vaccines versus the diseaes they prevent (with some exceptions where he did not find the data).

So, it seems difficult to conclue that the second premise supporting the core vaccine-autism claim holds up under scrutiny. Even though the number of vaccines that children receive has increased, the actual burden on their immune systems is lower now than it was when the only pediatric vaccine was for smallpox - and it is certainly far lower than if they actually got any of the diseases which vaccines prevent.

Premise 3: Parental Concern
The most personally-compelling premise supporting the core claim of the vaccine-autism connection consists of the aggregate of anecdotes from parents or pediatricians claiming to observe children developing, seemingly normally, right up until they get vaccinated - at which point their development halts or even regresses, and sooner or later, the dreaded autism appears on the scene.

However, as I noted yesterday, anecdotes are not always reliable because of cognitive biases, post hoc/cum hoc reasoning, and the tendency for memory to alter over time.

Also, the CDC and the Autism Science Foundation note that autism has a strong genetic component, and the CDC even states:

There is some evidence that the critical period for developing ASDs occurs before birth. [Emphasis mine.] However, concerns about vaccines and infections have led researchers to consider risk factors before and after birth

(An aside: this blogger, who contributes on many science and medicine blogs on this and other topics, notes that "The most characteristic feature of ASDs is a larger brain[viii], with smaller and more numerous minicolumns.[ix]" [Roman numerals in square brackets are blogger's citations to references in the post's footnotes.] The point he is trying to make is that this characteristic feature is the result of developments in utero, and ergo are not terribly supportive of the notion that autism is something that happens to people because of some triggering event such as vaccines. While some of this blogger's hypotheses and conjectures with regards to nitric oxide seem a bit far-out to me, he at least has a better grip on basic physiology than almost any anti-vaccine activist.)

So, it is not exactly clear that the compelling anecdotes offered up as a premise of the vaccine-autism claim are an accurate reflection of the etiology of autism spectrum disorders.

Conclusion?
The observations leading to the conclusion that vaccines are a causal factor in autism are no longer as secure as they may have once appeared. What of the core claim itself? Even if the premises of an argument are found to be false, or if the conclusion does not follow from them, it may yet be a correct statement of fact.

As I have noted, obliquely, in the links to literature above, numerous attempts to track down a causal relationship between vaccines and autism have failed to turn up much.

The most recent study to fail to find a causal link is Price et al 2010 (see analysis by someone more qualified than me). For more studies, check the topic reference at Science-Based Medicine.

As you will know from Tuesday's post, some of the most highly-touted studies by the anti-vaccine movement have been found to have rather glaring methodological flaws.

To sum it up: the bulk of the scientific evidence does not support the claim that vaccines are a causal factor in the development of autism spectrum disorders. As a non-scientist layman, I can sum it up as follows: this is as close to saying "vaccines don't cause autism" as makes no difference.

Trapped in the Anti-Vax Nexus


If you want an astonishing example of the power of confirmation bias, you need look no further than those who remain trapped in the Anti-Vax Nexus, and the consequences of its persistence.

Despite the fact that the three observations leading to the claim of a vaccine-autism link are on shaky ground and the fact that the core claim itself remains unsupported by a satisfactory base of evidence, anti-vaccine activists who are part of the Anti-Vax Nexus persist in propagating this claim.

There is, I think, a continual radicalization involved in this perseverance, which I think is made plain in the Age of Autism post I linked to yesterday. The radicalization goes in two directions (although, to quote the Scarecrow, "people do go both ways"):
  1. Epistemological Relativism
  2. Conspiracy Theory

Epistemological Relativism
Put simply, anti-vaccine activists who argue towards epistemological relativism are arguing some variety of 'science doesn't know everything', usually followed by some defence of rather less rigorous methods of accumulating and analyzing data.

While this statement is, strictly speaking, true, it is hard to see how this relates to the vaccine-autism link. I would think that the etiology of autism is a mystery that scientific inquiry can feasibly unravel (and indeed, as noted in links above, progress continues to be made). As part of that process, hypotheses for the etiology of autism (such as vaccines as a causal factor) will be proposed, analyzed, and either accepted, modified, or rejected.

The ultima ratio argument for epistemological relativism, of course, comes from academic post-modernism. Blogger Prometheus complains about this phenomenon here.

Consipiracy Theory
The other line of argument used to prop up the core vaccine-autism claim is the allegation of conspiracy, one featuring vaccine manufacturers and the entire corpus of public health officials, from the WHO on down through national organizations to the pediatrician who administers vaccines according to his nationally-recommended schedule, to suppress the truth about vaccines and autism.

The mildest version of this accusation typically suggests the conspiracy exists to preserve the profits of vaccine manufacturers or the power of medical practicioners (or both). More extreme versions are known to circulate, as I think was made plain in yesterday's linked AoA post.

I will here let journalist Gwynne Dyer's counter to the 9/11 Truth conspiracy theory do the work of explaining why I find the argument alleging conspiracy unconvincing.

Consequences
What are the consequences of staying trapped in the Anti-Vax Nexus for the families of chidren on the spectrum and sympathetic contributors?

For starters, there are some of the consequences as I described on Tuesday:
  • Diversion of Research - Instead of supporting research into the etiology and epidemiology of ASDs and how to mitigate the most disruptive effects of the disorders upon their children, people trapped in the Nexus continue to agitate in favour of further research into the vaccine-autism link.
  • Spread of Infectious Disease - The shared beliefs and shared sense of persecution can lead to people in the Nexus associating frequently with one another, which can lead to clustering of vulnerable individuals, ideal for transmission of disease. Since being trapped in the Anti-Vax Nexus entails adoping anti-vaccine positions, insofar as these positions result in reduced vaccine uptake generally, they further the spread of disease in wider communities.
  • Ethical Deterioration - The commentary following the Age of Autism post I linked to yesterday and the links I provided on Tuesday are, I think, sufficient to demonstrate this process in effect among those who are unfortunate enough to become trapped in the Nexus.

Among other possible consequences, I would like to highlight the following:

Autism Quackery
Because the Anti-Vax Nexus supports science denialism, families trapped in the Nexus are vulnerable to the mercantile opportunism of denialist quacks, who offer them all manner of unsupported, ethically dubious, and, of course, hideously expensive treatments to "save" their children or "recover" the child who was "lost" to autism (here I am definitely using scare quotes).

Prometheus has a category of posts describing the variety of quack treatments used to "treat" autism (scare quotes again, I don't know what is getting into me).

(Incidentally, one reason I like to cite Prometheus is because, in his own words: "Before someone accuses me of gloating or schadenfreude, let me say that I was one of those parents who bought the false hope [Emphasis mine.] and experienced the cognitive dissonance. I have immense sympathy for parents who find themselves in the same position today (or tomorrow). My purpose is not to ridicule them but to help them to find a way out of their dilemma. I’ve been there and I know a way out.")

Escaping the Nexus


So there you have it: the Anti-Vax Nexus. At its heart is the assertion that vaccines are somehow responsible for autism, that they have somehow stolen away the perfect children of parents now trapped in the Nexus and replaced them with children on the spectrum, like changelings of old (now that I mention it, consider the possibility that the folklore of changelings may come from the existence of developmental disorders among children in historical times, before we knew about things like genes, neurology, and Asperger's).

As you will hopefully have seen from this review, the core claim that props up the Nexus is based on shaky premises and is not supported by enough evidence to continue to be a serious contender as a hypothesis worthy of further ASD research.

To get around this problem, people trapped in the Nexus will, under the influence of confirmation bias, tend to radicalize until they are engaged in outright denialism with regards to the available scientific evidence (and some do not stop there, unfortunately).

Unfortunately, the consequences of getting and remaining trapped in the Nexus are pitiable: families trapped in the Nexus are at a higher risk of suffering from infectious disease, they are at a higher risk of getting caught up in unsavoury activity, and they are at a higher risk of being mmercilessly fleeced by quacks and charlatans who are more than willing to profit off of parents' hopes for complete recovery.

In the end, the best thing we can do is to try and help parents escape the Nexus, which I hope to touch on in tomorrow's post on responses to anti-vaccine activism.

1 comment:

  1. Yet another reason to dislike postmodernism. Have you read John Searle's Mind, Language, and Society? In it he tells the story of debating with a peer (who appealed to one of the most extreme ideas of postmodernism, the social construction of reality) and saying something to the effect of, "So if we went outside one night and looked up at the moon, would you tell me that we created it by agreeing it was there?" To which his interlocutor replied, "Yes."

    ReplyDelete