The anti-vaccine community are a loose collection of individuals and organizations who, at their core, are dedicated to the notion that vaccines are bad. There is some variation of opinion within the anti-vaccinationists, but not much. Some claim that vaccines do not work at all, while other acknowledge some benefit. Some try to be coy by saying they are just asking questions (sure, like the 9/11 truthers are “just asking”), while others come right out and make demonstrably false claims, like vaccines cause autism. But they all cluster around the opinion that vaccines are toxic (in some way) and that they cause harm.

What is remarkable about the anti-vaccine crowd is their consistency in talking points. One might call it message discipline (enough to make Republicans jealous) but I think that implies more deliberate coordination than there is evidence for. I may be wrong in this, but I think it is enough to say that they all travel in the same virtual circles and play off each other’s rhetoric and arguments. They are a political/ideological community, and such communities are more plugged in today because of Web 2.0 than ever before.

I’m not just talking about slogans, like “Green our Vaccines”, which are designed for widespread use. Reading the various anti-vaccine websites and authors you begin to see a pattern of specific talking points coming in waves.  Squalene has been in vaccines as an adjuvant for years, yet suddenly many of the anti-vaccine sites are squawking about squalene. I have not tracked down the original source of the squalene flap – it spread so quickly through the anti-vaccine blogs.

The job of the science-blogging community has been to analyze the anti-vaccine talking points when they crop up, and to provide some actual scientific information to balance the fear-mongering of the anti-vaccinationists. With regard to squalene, for example  – this is a naturally occurring organic molecule that is made in the liver and has been used safely in vaccines for years without any adverse events. I think the fear-mongering about squalene may have been triggered by a report that Gulf War veterans had anti-squalene antibodies from the squalene in the vaccines they received, and that this might have caused Gulf War syndrome. As it turns out, there never was squalene in the vaccines the Gulf War veterans received, anti-squalene antibodies occur naturally and seem to increase with age, and have no association with vaccines. So every single element of the anti-squalene fear was factually wrong, but the anti-vaccine movement got a cycle of fear-mongering out of it, and now squalene is permanently on the list of potential toxins in vaccines (substances are added to the list, but never removed, even when they are cleared as safe).

Another talking point I have seen crop up recently, on the Age of Autism blog and elsewhere, is the minimizing of the evidence for the safety of vaccines, and specifically the lack of association with autism, as only dealing with one vaccine (the MMR) and one ingredient (thimerosal). David Kirby, writing for the (in my opinion) anti-vaccine and anti-science-based medicine Huffington Post, recently wrote:

To begin with, it is unscientific and perilously misleading for anyone to assert that “vaccines and autism” have been studied and that no link has been found. That’s because the 16 or so studies constantly cited by critics of the hypothesis have examined just one vaccine and one vaccine ingredient.

Kirby was discussing the recent study that purports to show an increased risk of autism-like features in monkeys who received the Hepatitis B vaccine. David Gorski has already dismantled this study here, so I won’t repeat it.

I was struck when reading this that I had been reading almost the exact same phrase from J.B. Handley over at the anti-vaccine site Age of Autism – a remarkable consistency of talking points. This particular point is a manifestation of moving the goalpost – no amount of evidence, of course, will clear vaccines in the eyes of the anti-vaccinationists. Let’s review a bit of history.

The oldest reference I can find to a possible link between vaccines and autism is a case report from 1976 of a child who was diagnosed with autism following a smallpox vaccine – the report concluded that a causal association was unlikely. Then there is nothing until the Andrew Wakefield study in 1998 which started the autism-MMR vaccine scare. In other words, until Wakefield raised the concern of a possible connection between vaccines and autism, there was no reason to suspect a connection. There was no basic science or epidemiology suggesting a connection, and vaccine monitoring had not triggered any red flags about autism or other neurodevelopmental disorders.

The anti-vaccine movement, which was already in existence, picked up on Wakefield’s study and (true to form) that became their latest talking point of fear about vaccines. They made the argument in retrospect that the increasing vaccine schedule of the 1990s correlated with the increasing autism diagnosis rates of this same period. Subsequent studies (summarized here) both invalidated Wakefield’s conclusions and showed that the MMR vaccine is not associated with autism.

But autism was now on the radar of the anti-vaccine movement, so they turned (without really ever giving up on MMR) to a vaccine ingredient, thimerosal, which is a mercury-based preservative in some vaccines (and, interestingly, never in the MMR vaccine). There already was in existence an anti-mercury community who had been fear-mongering about environmental mercury for years. At this point I have to say that, yes, mercury is a neurotoxin, and it is absolutely legitimate to study the effects of mercury and to limit all cause human environmental exposure to mercury. That’s all good. But it seems to be human nature that for every legitimate point there is a person or group who will take it to extremes. Mercury is a toxin, but toxicity is all about dose. The mercury-militia, as they are sometimes called, went beyond science and reason by blaming sub-toxic levels of mercury for whatever they could think of.

Needless to say, the anti-vaccine movement and the mercury militia became quite cozy over the issue of thimerosal. What is disturbing is that they have also infiltrated the autism community, and now do their best (much to the annoyance of many in the autism community) to equate autism awareness with anti-vaccine and mercury fear mongering.

In any case – fear over thimerosal exposure and autism was raised by the anti-vaccine movement, so this fear was addressed. Numerous studies have now shown no association between thimerosal exposure and autism or other neurodevelopmental disorders. The most devastating evidence was the near complete removal of thimerosal from vaccines in the US by 2002, which in the subsequent seven years had zero effect on the rate of increase of autism diagnoses. David Kirby (who did much to fan the flames of fear of thimerosal) and others predicted autism rates would plummet – they didn’t.

As an aside, the increasing rates of autism diagnoses has also been studied, and at present the consensus of scientific evidence is that the apparent increase is mostly or entirely due to a broadening of the definition of autism and increased surveillance.  True autism incidence appears to be flat over time.

Now Kirby and others are shifting to other vaccines and other vaccine ingredients. Why? There never was any reason to suspect vaccines as a cause of autism in the first place. True autism incidence is not even increasing. There is no credible data to link vaccine and autism. The consensus of evidence is that autism is dominantly a set of genetic disorders (not a single disorder or disease). There is no compelling evidence for any significant environmental factor in autism, although minor environmental factors cannot be excluded.

So you see the rhetorical trick that Kirby and Handley are playing – the published evidence only excluded MMR and thimerosal as causes of autism – not the other vaccines or vaccine ingredients. Their unstated major premise (the one they want to slip in the back door) is that there is some reason to suspect vaccines as a cause of autism in the first place.

The reason they are likely to cite is the anecdotal observation of parents that symptoms of autism appeared at or around the time of receiving a vaccine. They will make such arguments as emotional as possible – scientists are not listening to mommies, and mommies know their children. Yes, but mommies are human and subject to all the errors of observation and thinking that plague our species. It turns out that subtle signs of autism are present long before parents recognize them – even before the vaccines they blame were given. Plus, if Kirby and Handley are now willing to admit that MMR has been cleared (I don’t think they are, but that is what the “one vaccine, one ingredient” argument would imply) then they also have to admit that all those parents who observed that their child’s autism began in temporal correlation with the MMR vaccine were either wrong or victims of a coincidence of timing.

What this reflects is that the anti-vaccine movement is not intellectually rigorous or, in my opinion, even honest. They grab onto whatever argument they can, even if there is a lack of internal consistency. It is like the famous kettle defense – when an attorney puts forward several defences of their client, all of which are mutually exclusive.

Another flaw in the one vaccine, one ingredient notion is that if the MMR vaccine has been cleared by the evidence, then doesn’t that also clear all of the ingredients of the MMR? Of course, many of those ingredients are the same as many of the other vaccines. At least we can say that the evidence suggests a lack of toxicity from any of the ingredients in the MMR in the doses present in the MMR.

The strategy the anti-vaxers use for such arguments is to deny reasonable applications of the dose response that we would expect from all pharmacological effects, including toxicity. In other words, the greater the dose of the toxin the greater the toxic effect should be – in this case the risk of autism or neurological disease should increase with dose, not be flat. Anti-vaxers routinely deny this basic and generally accepted fact of biology. For example, when a study showed that doubling the dose of thimerosal had no effect on adverse outcomes, they argued that the study is useless because there wasn’t a zero thimerosal control. This blatantly denies the fact that doubling the dose of a putative toxin, in the dose range that causes toxicity, should increase the toxicity. This is one of the lines of evidence that is actually required in order to scientifically establish toxic cause and effect.

So for any ingredients that MMR shares with other vaccines, the addition of MMR should add to the toxicity (for example increase the risk of developing autism) but studies have not detected any such effect. So it is not fair or accurate to say that the evidence has looked at only one vaccine and one ingredient.

It should also be pointed out that there are vaccine monitoring systems in place. These systems are not looking for a particular correlation with vaccines – they are looking for any correlation. If there were a significant increase in the risk of developing autism from vaccines, these systems should detect it.

The moving the goalpost strategy will work forever with the anti-vaccinationists, because there is an astronomical number of permutations of vaccine ingredients, specific vaccines, and possible target diseases and disorders. We will never have definitive evidence specifically ruling out every possible vaccine combination for every possible disease. The same is true, of course, for every single medical intervention.

For example, in France anti-vaccine concerns focus on multiple sclerosis, not autism. So antivaxers in the US and UK can simply migrate over to MS once they run out of steam on autism fear-mongering.

What we do have are studies and monitoring systems looking for any signal of adverse events peaking above the noise in the data. We will also chase down any specific hypotheses that crop up. The data shows that vaccines are very safe, and despite very rare reactions to vaccines (which are acknowledged and compensated) there is no credible evidence to correlate vaccines and autism or neurodevelopmental disorders. The specific hypotheses of MMR and thimerosal have been directly studied and the evidence strongly supports a conclusion of lack of correlation.

Despite Kirby’s claim that such statements are unscientific – a fair look at all the evidence supports the conclusion that there is a lack of association between vaccines and autism. Further, there is no reason to hypothesize that there would be such a link, and further still there is compelling evidence that true autism rates are not increasing, and that autism is dominantly genetic in origin.

Responsible scientists look at the totality of evidence to make an internally consistent argument.