Friday, December 09, 2005

Thimerosal and Autism: Where are the Goal Posts?

Kevin Leitch is a parent of an autistic child, and an outstanding blogger, who is highly skeptical of claims that thimerosal in vaccines causes autism. Leitch has commented here, and in greater detail here, on my previous post about a recent admission by David Kirby, author of Evidence of Harm, a book highly sympathetic to claims that thimerosal causes autism. Kirby now admits that if autism cases among 3-5 year olds don't start declining by 2007 (in response to the removal of most thimerosal from vaccines), "that would deal a severe blow to the autism-thimerosal hypothesis."

Leitch points out that Kirby has moved the goal posts. Earlier this year, the New York Times summarized Kirby's position as follows:
Because autism is usually diagnosed sometime between a child’s third and fourth
birthdays and thimerosal was largely removed from childhood vaccines in 2001,
the incidence of autism should fall this year.

That's this year-- 2005. Leitch rightly asks, "what are the extra two years for." This is how Kirby explained his current position to me (without explaining why it has changed) in an e-mail back in August:

It is a myth that "most" mercury came out [of vaccines] in 1999. It wasn't even until July of 1999 that the government suggested that manufacturers begin to remove the
mercury "as soon as possible." Factories did not get approval for, and begin making thimerosal-free vaccines until 2000 at the earliest (Except for Merck, which got approval in Sept. 1999 to make Hg-free Hep-B vaccine, though it is not clear when this new formula actually appeared on the shelves of doctors offices).

On Meet the Press, Dr. Fineberg said that some mercury containing pediatric vaccines expired in 2003. I have reason to believe it was later than that, as many vaccines without thimerosal were not even produced until 2001 or 2002, and most vaccines have a shelf life of about three years from manufacture, it is my understanding. (Again, correct me if I am wrong). Plus, it takes quite some time for new lots to work their way through the distribution system, and new stocks are not ordered until old stocks begin to run low, as far as I can discern.

By this account, there were still mercury-containing vaccines on the shelf, potentially at least, until very recently. This matter is being investigated right now by the United States Senate, and we should have an answer soon, even if the Senators must subpoena the information (which they will, their staffs have indicated).

But let's take Dr. Fineberg at his word for now. He said at least some mercury containing vaccines (we don't know how many because the FDA won't say) expired in 2003. Meanwhile, 3-5 year old children entering the system now were born no later than June, 2002. In fact, we don't have the breakdown of individual birth cohorts, but one would imagine that there were more five year olds (born in 2000, when many kids were still getting the full amount of mercury in their shots) entering the system last quarter than three year olds, born in 2002. However, early intervention programs are lowering the age of diagnosis, and perhaps this ratio is changing as well.

. . .

My guess, and it is admittedly a guess, is that MOST 3-5 year olds entering the system today, on average received relatively high levels of mercury in their vaccines. If the FDA would release the pertinent information, we would know exactly how much that was.

So Kirby says that maybe thimerosal wasn't removed from vaccines in 2001 after all. Maybe it wasn't mostly removed until 2002 or 2003.

I don't find this persuasive. Proponents of the thimerosal-autism hypothesis hold that increased exposure to thimerosal resulting from changes in infant vaccine schedules in the early 1980s caused a massive subsequent increase in autism incidence. It isn't that there was no thimerosal exposure prior to 1980 (there was), it's that the increased exposure supposedly caused more autism. So significant decreases in exposure, even if some exposure remains, ought to decrease autism incidence if the hypothesis is correct.

Moreover, as an informed correspondent has told me, there was a shortage of DTP vaccine in 2001 and 2002, so it's unlikely that there was old vaccine sitting around by 2003. But Citizen Cain is a patient man. I can wait until 2007. I'm just afraid that by then the new hypothesis will be that miniscule amounts of thimerosal, still present in some vaccines because of use during the production process, are sufficient to cause continued high incidence of autism.