Mercury in vaccines: Changing perspectives, changing minds

The Pediatric Insider

© 2013 Roy Benaroch, MD

News from the vaccine world: The AAP has announced that it supports the WHO’s position that the mercury-containing preservative, thimerosal, is safe, and should continue to be used in vaccines.

The first I can recall hearing the word “thimerosal” was on a bottle of contact lens solution, as a teenager. “Does not contain thimerosal”, the container said. “Safe and gentle on eyes.” What was this thimerosal, and if it could hurt my eyes, why would anyone put it in contact solution?

Thimerosal has been around since the early 20th century, used as a preservative to prevent the growth of bacteria and fungi in sterile solutions. It is, objectively, phenomenally safe—no study has ever found a toxic effect of this stuff in humans at anywhere near the amounts that we’ve ever been exposed to it. We know it can prevent multi-dose vials of vaccines (and other injectables) from developing dangerous contamination, and we know how to safely use it in manufacturing and producing health products. It’s cheap, it’s safe, it works. So what’s the problem?

The problem is mercury. Thimerosal contains an organic compound called “ethyl mercury”. Though ETHYL mercury has a very low potential for toxicity, similarly-named METHYL mercury is an industrial pollutant that can cause neurologic damage and other problems, especially with high or prolonged exposures. But METHYL isn’t ETHYL, any more than ETHANOL (=ethyl alcohol, found in beer, causes drunkenness when consumed in ordinary amounts) is the same as METHANOL (=methyl alcohol, which can make you blind and dead if you drink just a little.)

Nonetheless, “mercury” is scary, and in 1999 the AAP and the CDC agreed that it would be safest for mercury-containing preservatives to no longer be used in children’s vaccines. And over a few years, that’s what happened. Vaccines were switched to be produced in more-expensive, single-use vials. It wastes a lot of glass, but you don’t need a preservative if a vial is only used once.

Once concerns about mercury began to swirl, a vocal segment of the autism community latched onto mercury as the cause. Despite removing mercury from all vaccines (except some flu shots), the rates of autism have continued to increase. There has never been any evidence of any harm from the mercury that had been used, and most of the autism community has moved on past the mercury idea. Worth looking into? Yes. Plenty of evidence that mercury’s not the culprit? Yes. Time to pursue other leads? Yes.

(As a side-note, based on a fraudulent 1998 paper some began to think MMR was an autism trigger. That has also turned out to be false. Ironically, no MMR vaccine ever contained any thimerosal. Still, the “mercury” and “MMR” media circus kind of intertwined and mixed up the stories, leaving parents breathless with unnecessary worry. Way to go, media.)

What have we learned since the removal of thimerosal from American vaccines in 1999? Autism rates have not decrease (they’ve continued to increase, perhaps even faster than before.) No evidence of any harm from thimerosal exposure has ever been uncovered. Extensive studies have supported the safety of the preservative, showing, for instance, that it is quickly and easily excreted from the body. It’s an academic point in the USA, anyway: thimerosal is not coming back.

But what about the rest of the world? We’ve got plenty of money, here, to be extra-cautious (or extra-indulgent of worry, perhaps.) But making single-dose vials of vaccines costs a whole lot more, and there is no practical, proven, safe alternative as a preservative for vaccines. So the same AAP that in 1999 suggested that the US stop using thimerosal is now saying that it’s OK for everyone else. I know: sounds dubious. But I think given what we’ve learned and confirmed about thimerosal’s safety, the AAP made the right call.

Detailed review from CDC

Long article reviewing vaccine-autism speculation

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