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December 3, 2002
Doing Justice to Thimerosal, And the Story
Like Charles Murtaugh, I've been trying to get around to writing something about the thimerosal issue for some time. There are so many angles to the story that it's hard to know where to begin. They are, in no particular order:
Is thimerosal safe?
Was it safe when kids didn't get so many vaccines, but became less so as the exposures multiplied?
If it isn't safe, what does it do?
Is it a cause of what some people call an autism epidemic?
Is there a rise in autism, or just a rise in its diagnosis?
If there was harm done, who bears the blame for it?
Who put the paragraphs into the homeland security bill that seem to let Eli Lilly off the hook for thimerosal lawsuits?
When and how should vaccine makers be insulated from legal action, anyway?
And that's just off the top of my head. But I wanted to point out that some new data may be helping to clear things up, at least those first couple of points. Last year, the Institute of Medicine issued a lengthy report that basically said that there was no evidence that thimerosal, even when given in multiple vaccine doses, was harmful. But there was no evidence that it couldn't cause harm, either, and organomercury compounds are known to be trouble, in principle. Thus the recommendation that it be phased out, under the better-safe-than-sorry principle.
The University of Rochester studied 61 children who had received thimerosal-containing vaccines. Blood levels of mercury were lower than expected, well under the toughest EPA standards. And the mercury was found to be cleared much more quickly from the children's system than had been expected (a week versus the predicted 45 days.) This goes a way toward clearing things up, because it makes it less likely that there's an accumulation of mercury with multiple vaccinations. A key part of the anti-thimerosal case has been that exposure to it was allowed to creep up over the years - the hypothetical autism epidemic is much more recent than the use of thimerosal per se.
Anti-thimerosal groups point out that we still don't know what the peak levels of mercury are in the blood after dosing, which is true (although there are studies in the works to check that.) But the entire story, to my medicinal chemist's eye, is based on the med-chem properties of clearance and area-under-the-curve (AUC,) rather than Cmax (peak concentration.) And that is addressed well by the Rochester work. I look forward to seeing more data, but I think that the odds are heavy that thimerosal isn't doing harm. (I'll reserve judgment on whether some people are possibly much more sensitive to it than others - not impossible, but not proven.)
And I'll close by mentioning a not-unrelated fact: when you search "thimerosal" on Google, the first ad that appears on the right-hand side of the screen is for "Thimerosal attorneys." I'm not saying that inserting the stuff into the Homeland Security bill was a good idea, because it wasn't. It makes everyone look guilty, like there's something to hide. And I really don't think there is. The industry has enough problems without bringing more down on its head.
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