written by Tara Haelle

Hang on tight, friends! This is a long post – but an important one – about several articles published in Pediatrics today that could affect the protection of children everywhere from vaccine-preventable diseases. If you’ve ever had questions about thimerosal in vaccines, this post may address some of those questions as well.

All three Pediatrics articles deal with the same thing: an international treaty drafted by the United Nations Environmental Program‘s Global Mercury Partnership to reduce mercury pollution and environmental mercury exposure across the world. Great! This is an important and valuable initiative – except for one part. As part of the treaty, the UN wants to ban the use of thimerosal, a mercury-containing preservative, used in vaccines. Not good. The short version for why? This proposed ban threatens millions of children’s lives across the world, including children in the U.S. and in other developed countries. I’ll get to the long version in a moment.

First, the World Health Organization and American Academy of Pediatricians (AAP) have already pushed for the thimerosal ban provision to be removed from the UN treaty. But today’s three AAP articles drive the point home. One of these provides some historical context for why thimerosal was removed from childhood vaccines in the U.S. (as recommended by the AAP and the U.S. Public Health Services in 1999) and in other high-income countries. The other two emphasize just how important it is – and how ethically essential it is – that the ban not be included in the UN treaty.

Here’s the back story:

A 1997 US FDA review of the mercury content in products revealed that the amount of thimerosal in childhood vaccines could, possibly theoretically, build up to exceed the EPA’s guidelines (but not the FDA’s guidelines or those of the Agency for Toxic Substances Disease Registry) on safe exposure limits for inorganic mercury, called methylmercury.

Methylmercury is the neurotoxin you hear about when you’re warned not to eat too much fish (especially while pregnant). Back in 1999, scientists knew a lot about methylmercury, but they didn’t know much about ethylmercury, the type in thimerosal. As Dr. Louis Cooper and Dr. Samuel Katz, both involved with the 1999 recommendations, put it, “the absence of clear data for ethyl mercury did not allow any assumption to be made about its safety.”

Meanwhile, debates were raging in Congress about concerns over vaccines and autism, fueled by the now-retracted and thoroughly debunked (pdf) study by Andrew Wakefield linking the MMR vaccine to autism. Parents were scared and confused. Media coverage was exacerbating the impression that public health officials weren’t being forthright about vaccine risks.

So, poof! All thimerosal was pulled from childhood vaccines except the multi-dose flu vaccine, since kids getting that would only get amounts below the EPA guidelines for methylmercury (even though, again, thimerosal is ETHYLmercury).

Now fast forward to today. We know a LOT more about ethylmercury: namely, that it’s not as bad as methylmercury and sails through our bodies a lot more quickly. In fact, methylmercury’s half-life is about seven times that of ethylmercury, which does not build up in the body like methylmercury does.

“There is no credible scientific evidence that the use of thimerosal in vaccines presents any risk to human health,” writes Dr. Katherine King in one of today’s Pediatrics articles. Dozens of studies and a massive review at the Institute of Medicine back this up.

Thimerosal in vaccines is not a problem. But what is a problem is thimerosal’s PR image. Again, from one of today’s AAP articles: “Given the complexity of the science involved in making guidelines, the polarity between vaccine advocates and those believing their children have been harmed, the media’s attraction to controversy, and, in retrospect, inadequate follow-up education about the issues to clinicians and the general public, it is not surprising that the steps taken left misunderstanding and anxiety in the United States and concerns in the global public health community.”

Basically, they’re saying, yea, we kinda screwed up with conveying that thimerosal really IS safe after all. We wanted to be over-cautious before, and we were, and that was good, but now we’ve sorta dropped the ball on following through in letting you know that YOU HAVE NOTHING TO WORRY ABOUT with the ethylmercury in thimerosal. As Dr. Walter Orenstein puts it, “Had the evidence that is available now been available in 1999, the policy reducing thimerosal use would likely have not been implemented. Furthermore, in 2008 the World Health Organization endorsed the use of thimerosal in vaccines.”

But apparently, the WHO’s endorsement can’t overcome thimerosal’s PR image problem in the eyes of the UN. And so the UN is short-sightedly and dangerously trying to ban thimerosal in vaccines.

Well, that just means getting rid of it in flu vaccines (many of which don’t even have thimerosal since they’re single-dose), so what’s the big deal anyway? The big deal is that not all countries got rid of thimerosal in their childhood vaccines. Many high-income countries like the U.S. did – because they could afford to be overly cautious.

But more than 120 middle- and low-income countries – including the developing countries where vaccine-preventable diseases have the highest rates of infection and death – have continued using thimerosal-containing vaccines because the preservative allows them to make cheaper vaccines that withstand less rigorous storage without compromising safety.

Getting rid of thimerosal would mean overhauling vaccine production and storage in those countries, which the WHO estimates would cost more than $300 million for vaccines supplied by UNICEF or the Pan American Health Organization alone. As Dr. King argues, “it is banning thimerosal that would cause an injustice to those living in low- and middle-income countries and relying on these vaccines for effective protection against many harmful infectious diseases.”

Why does this matter to people in the U.S. or in other higher income countries? Because we live in a global world. Vaccines with thimerosal are currently used to immunize about 84 million children across the world every year, saving an estimated 1.4 million lives from vaccine-preventable diseases. That includes lives saved in developed countries, where a future outbreak could potentially be imported from other countries in which a vaccination program may have ceased following a thimerosal ban.

More simply put: If the UN forces the removal of thimerosal from vaccines, then 84 million children risk not getting vaccinated (and/or vaccinated on time) due to delays in vaccine production or due to a shortage of vaccines because of increasing costs. This, in turn, could (and likely would) mean an increase in vaccine-preventable infections, which will, in turn, kill more children worldwide and risk disease carriage to other countries. Like here.

And even if we pretend that any outbreaks in other countries will remain there without reaching our shores (and/or that we simply don’t care about millions of children dying of these diseases elsewhere), a thimerosal ban in vaccines could still be a problem for developed countries. In an emergency, as Dr. Orenstein and colleagues argue, not being able to manufacture vaccines with thimerosal could endanger lives during an epidemic if it slows down vaccine production. So yes, this is something you should care about.

Dr. Cooper and Dr. Katz – again, both pediatricians who were closely involved in the original 1999 decision to pull thimerosal out of vaccines – sum it up best: “The World Health Organization recommendation to delete the ban on thimerosal must be heeded or it will cause tremendous damage to current programs to protect all children from death and disability caused by vaccine-preventable diseases.”