Thimerosal and autism: two questions

The last few days have been hectic ones. Circumstances conspired again to turn me, almost against my will, into a vaccine blogger, leading me to step with both feet into the mercury-autism controversy with this post and this followup, the combination of which have brought more attention to this blog than anything I've ever written before. I honestly didn't expect to make my first big splash in the blogosphere on this topic, but c'est la vie. Fortunately, most of the responses were, surprisingly, less hostile and more supportive than I had feared they would be. However, the sheer hostility of a small minority of responses was amazing. For example, someone calling him or herself "cellis" said something that very much reminds me of the sorts of abuse anyone who points out how weak the evidence for a link between mercury and autism can expect, similar to what Kathleen Seidel wrote about in her open letter to David Kirby. Cellis said:

As for the original creator of this absurd post (and all you other ignorant morons), I just hope you have a child or grandchild with autism in the very near future so that your small minds will be blown away when you finally wake up and realize how they got that way...which, since the rate has now "miraculously" risen to 1 in 150 children, I'm sure someone you care for will be affected very soon...Karma's a bitch. Can't wait to see you eat your very ignorant and uneducated words.

There's more where that came from, some even just overnight. I tell you, it's almost enough to make me go back to blogging about less controversial topics, like, say, creationism (or maybe Terri Schiavo). At least creationists usually offer to pray for me, rather than angrily and gleefully wishing autism on my or other people's children just to "teach us a lesson." It half makes me hope that my joke about wanting an Instalanche doesn't come true. But, before I attempt to move on to other topics, I can't resist one last post. (Whether I succeed in moving on is another issue entirely, but I'm going to try; as I pointed out less than three weeks ago, vaccine hysteria was never intended to be a primary focus of this blog. I'm sure I'll end up coming back to the issue sooner or later, but I need a break. Also, this has delayed the writing of a series of posts I've wanted to do for almost two weeks now.)

I've been trying to think of a way to boil the whole issue down to its utter essence, as one commenter suggested. However, I'm going to do it a little differently than what the commenter had in mind. I think two questions serve that purpose quite nicely:

1. What evidence would convince me that the Geiers and Boyd Haley and all the others who are so convinced that mercury in thimerosal used as a preservative in vaccines is a major cause of or contributor to autism are correct and that my skepticism is ill-founded?
2. What evidence would convince those of you out there who are utterly certain that thimerosal in vaccines either causes or is a major contributor to autism that there is no link between mercury in vaccines and autism?

Pretty simple questions, aren't they? I bet some won't find them that easy to answer. Let's see how intellectually honest I am and mercury-autism advocates are, comparatively speaking.

For my part, I can answer my question fairly easily. There is indeed something short of having an autistic child that could make me "eat my very ignorant and uneducated words," as cellis put it. Thimerosal has been removed from vaccines in the U.S., and the last lot of thimerosal-containing vaccines expired in January 2003. If indeed mercury in vaccines causes autism, then five years from now and ten years from now the rates of new cases of autism should plummet dramatically and unambiguously. That they have not done so in Canada or Denmark, both of which removed thimerosal from their vaccines in the 1990's, suggests that it's highly unlikely that the U. S. will see a major decrease in new autism cases over the next decade. However, I'm willing to start fresh and, for the sake of argument, for the moment take on the attitude that seems to be implied by the willingness of activists to dismiss teh Danish and Canadian data so blithely: namely, that it doesn't matter unless it happens in the U.S. But how much is enough? I propose as quite a reasonable measure that, if autism rates fall by 50% or more in 2010 or even 2015, I will happily admit that I was incorrect in my assessment and rejoice that such a blow has been struck against this condition. If rates fall by less than 50% but still inarguably statistically significant, I will concede that this would be pretty good epidemiological evidence that there might be a connection, although in that case the connecton would clearly not be nearly as strong as the link claimed by some activists, like J.B. Handley, founder of Generation Rescue, whose website states quite bluntly that "childhood neurological disorders such as autism, Asperger’s, ADHD/ADD, speech delay, sensory integration disorder, and many other developmental delays are all misdiagnoses for mercury poisoning."

Given such rigidly dogmatic statements, question #2 takes on more importance. What evidence would convince someone like J. B. Handley to change his mind? I can't imagine what evidence would convince him, or Boyd Haley, or the Geiers. It also leaves the a followup question for those of you out there who are so sure that mercury in vaccines causes autism or is a major contributor to autism: Will you concede that you were incorrect if, in 2010 and 2015, autism rates in the U.S. remain unchanged or have increased? I don't have a lot of hope that you will, given the Canadian and Danish experience, where no decrease in autism rates have been observed several years after removal of thimerosal, but I hope I am wrong.

Simplistic?

Well, yes and no. For obvious reasons, it's impossible ever to do the gold standard study about this issue: a double-blinded randomized control trial comparing vaccination of babies with vaccines containing thimerosal and vaccines not containing it and follow the children prospectively to see if the babies receiving vaccines with thimerosal have a higher rate of autism than those receiving thimerosal-free vaccines. So what's the next best thing? Good epidemiological evidence has a way of trumping all the theoretical concerns, cell culture experiments, and even animal data, and the removal of thimerosal from vaccines two years ago provides an epidemiological experiment that is seldom possible to do with other diseases. It's a golden opportunity to test once and for all the hypothesis that autism is caused primarily by mercury in thimerosal in vaccines. If, after a decade of no thimerosal in vaccines, austism rates do not decline, that would be very strong evidence that mercury in vaccines is not and was not the cause of autism. In such as case, it would be very difficult indeed to say that there is a link between the two.

I'll even go out on a limb a bit here (well, probably not really). My prediction is that, in 2010 and 2015, autism rates will remain roughly the same as they are now or maybe somewhat increased, thanks to the continuing improvements in recognition and diagnosis. My further prediction is that, in 2010 and 2015, in light of the unchanging incidence of autism, the mercury-autism activists will either (1) still be claiming that mercury causes autism, (epidemiological evidence be damned) or (2) have changed their claim to say that it is something else in vaccines that is causing autism.

Anybody want to bet against those predictions? Think I'm being disingenuous? Tell me why.

ADDENDUM: OK, I changed my mind and posted on this issue one more time.