"I'll Take Thimerosal"

Once upon a time, when I was still misapplying the precautionary principle, I got very hot and bothered around this time of year. I wanted my kids to get the flu shot, but I had heard so many scary things about thimerosal and how certain of the flu shots still contained it as a preservative that I would grow very anxious. I'd call around, making sure the clinic had FluMist (no thimerosal) or an otherwise thimerosal-free vaccine, and I'd feel very proud of myself for doing my "due diligence."  I even advocated on my now-defunct blog Science for Sale for "demanding" thimerosal-free flu vaccine at your pediatrician's office or clinic.


Now I say to nurses: "I'll take the thimerosal version."

My fabulous vaccinated children (old picture!)

Well, that's a bit of an exaggeration--not to mention a bit of plagiarism on my part (co-founder of Moms Who Vax, Karen Ernst, was the first person I'd ever heard say she asked a nurse for "the thimerosal one" just to make a point). But not by much. Last week, my three-year-old daughter had her well-child checkup. I wanted her to get her DTaP booster early, because of pertussis outbreaks in Minnesota and beyond and because signs are pointing to the current vaccine losing effectiveness sooner than expected. She'll get that booster later this week, but I was able to get her chicken pox booster and her flu shot at this appointment. When the nurse came into the room with the syringes, she looked at me and said, almost apologetically, "We don't have any thimerosal-free flu shots right now." To me, this was about as meaningful as hearing at Starbucks "I'm sorry, we're out of whipped cream today."

It was only later that night that I marveled at how far I'd come since those days at the Target clinic when I fretted over my older child's flu shot. I've come so far because I finally understand how vaccines actually work, how their components work in our body, and how leaving my child even a "little unimmunized" is a serious health risk--one I'm no longer willing to take. (Risk analytics is a subject I wish I'd studied up on earlier in my parenthood.)

For those who don't know, thimerosal is a preservative meant to keep the vaccines safe. If vaccines didn't have preservatives, then you'd really start seeing some "vaccine injuries." The CDC states that thimerosal is "added to vials of vaccine that contain more than one dose to prevent the growth of bacteria and fungi in the event that they get into the vaccine." If you've been following the news, you are probably keenly aware that fungi in injectable medicines is a bad thing--just ask the hundreds of meningitis victims trying to get well right now. However, thimerosal is in almost no childhood vaccines anymore--not MMR, not DTaP, not Hep B. The multi-dose vial of flu shot is really one of the only shots that might contain thimerosal.

When people express concern about thimerosal, they often use the overarching term "mercury." These same people (and I was one of them) almost never know that there is a huge difference between ethylmercury and methylmercury. Some of us (ahem, me) didn't even know there was a difference at all. Even though they have similar names, they are completely different materials. Worth repeating: completely different materials.

The one that people often think of when they hear the word "mercury" is methylmercury. This is the stuff that can be found in certain types of fish, formed in environments where mercury metal exists. High levels of methylmercury can be harmful to the human nervous system, and although federal standards try to control the level of mercury in foods and environments, the truth is we are all exposed to some methylmercury. It's this--methylmercury--that too many people think is part of the thimerosal preservative.

It's not.

The multi-vial dose of flu vaccine contains trace amounts of thimerosal, which contains ethylmercury, which does not "build up" in your body like methylmercury and is easily excreted. It is worth repeating that methylmercury and ethylmercury are different chemical compounds. As the WHO states, "The half-life of ethyl mercury is short (less than one week) compared to methyl mercury (1.5 months) making exposure to ethyl mercury in blood comparatively brief. Further, ethyl mercury is actively excreted via the gut unlike methyl mercury that accumulates in the body." If you need any reassurance or your own personal "chelation therapy" following a visit to the National Vaccine Information Center, take a look at this study from the New England Journal of Medicine that shows ethylmercury having no neurological effect on children who received vaccines with a thimerosal preservative. (There are two more.)

But this is mostly academic, because thimerosal was taken out of the vast majority of childhood vaccines a while ago at the request of the CDC. This wasn't because thimerosal is dangerous. Instead, it was done--against the protests of science-minded organizations--because the CDC feared the anti-vaccine movement had simply poisoned too many minds in their completely erroneous and harmful accusations of some sort of link between thimerosal and autism. The CDC removed thimerosal from vaccines as a preservative because they wanted parents to continue vaccinating and were afraid that the misinformation about it was too entrenched. It was the first time in recent history that science bowed to pseudo-science in this way.

So when I get my flu shot without even wondering if it contains thimerosal or not--when my child gets a flu shot that contains it, even though it's becoming harder and harder to find a thimerosal-containing flu shot--a little part of me feels like I'm standing up for science. Because I am.