Friday, October 29, 2010

Thimerosal in Vaccines: Questions and Answers

As with most, antivaccinationists (or antivaxxers as they are so affectionately called), Mr. Hubbs often finds himself making claims about the effects of thimerosal in vaccines.  He refers to the (now discredited) Andrew Wakefield study which attempted to link thimerosal with autism along with speaking of newer Wakefield studies with primates trying to suggest this link actually exists.

Unfortunately for Mr. Hubbs, there is not one single peer-reviewed study in existence which proves such a link exists.  In fact, of the dozens of studies which tried to determine if such a link exists, they all have found no correlation between thimerosal and autism whatsoever.

So why is there so much focus upon thimerosal in the first place?  Well, the simple truth is thimerosal has been used as a preservative in vaccines since the 1930s and although there have never been any published studies indicating it causes autism (or is even linked to autism), thimerosal is composed of approximately 50% mercury by weight, and anytime you mention mercury it is going to raise alarms with the antivaxxers.

However the FDA has a fabulous Q&A page on thimerosal located here.  The page states that "as a vaccine preservative, thimerosal is used in concentrations of 0.003% to 0.01%. A vaccine containing 0.01% thimerosal as a preservative contains 50 micrograms of thimerosal per 0.5 ml dose or approximately 25 micrograms of mercury per 0.5 mL dose."  It should also be noted that due to the fear surrounding mercury and lowered EPA guidelines for mercury (the EPA's methylmercury reference dose is .1 micrograms/kg body weight per day) thimerosal has been phased out of childhood vaccinations as shown by this table.

So is 25 or 50 micrograms of mercury something to be concerned about?  Depends who you ask, but for all the attention given thimerosal by the antivaxxers, you might think they would care just a tad more about a simple can of tuna.  Why tuna?  Well as it turns out, a six ounce can of tuna contains approximately 52 to 60* micrograms of mercury which is more than vaccines with the highest levels of thimerosal.

I'm a "show your math" kind of person, so let me spell this out in detail.  First we need to define how much mercury is in the tuna, and for that we can use this chart provided by the FDA.  Reading that chart shows us that albacore tuna has 0.353ppm of mercury.

Now we need to determine how many grams of tuna are in a can.  For that we convert 6 ounces to grams and we come up with 170 grams (0.0352739619496 oz per gram).  So now we take that 0.353ppm of mercury in the tuna and multiply it by the number of grams and we get the answer of 60.01 (0.353 x 170).

So basically, there are 60 micrograms of mercury in one 6 oz. can of albacore tuna.  There is a bit less in light tuna, an a bit more in fresh tuna, but you get the idea.  In case you don't trust my numbers, here is another source.  I should note they determined there were approximately 52 micrograms in a can of tuna whereas my math above shows closer to 60, but their figures are from a study from 1993 (see reference below) whereas my figure is based upon updated FDA findings from a study performed in 2002-2004.

Long story short, if you are really concerned about the mercury in vaccines, you should be protesting at your local supermarket, because children are much more likely to be exposed to mercury via canned tuna than they are via vaccines, and it is safe to say people who like tuna and/or feed it to their children probably do so more than a few times in their lives, so imagine the cumulative effect of eating one can of tuna per week for an entire year - yet when is the last time you saw a conspiracy theorist website about how commercial tuna fisherman are trying to harm children in order to profit?  If one exists I surely haven't seen it.

However, research does continue on the usage of effects of thimerosal, and recent studies from the National Institute of Allergy and Infectious Diseases (NIAID) have continued to not find long term effects or negative side effects.  In fact, the FDA states the following:

"More recent NIAID-supported studies at the University of Rochester and National Naval Medical Center in Bethesda, MD examined levels of mercury in blood and other samples from infants who had received routine immunizations with thimerosal-containing vaccines. [Pichichero ME, et al. Lancet 360:1737-1741 (2002)] Blood levels of mercury did not exceed safety guidelines for methyl mercury for all infants in these studies. Further, mercury was cleared from the blood in infants exposed to thimerosal faster than would be predicted for methyl mercury; infants excreted significant amounts of mercury in stool after thimerosal exposure, thus removing mercury from their bodies."
So essentially if studies have not found impacts to children, and considering the rates of autism diagnoses have not decreased even though thimerosal is no longer in the vast majority of childhood vaccines... how can antivaxxers like Mr. Hubbs still be arguing that thimerosal causes autism?  If they feel it is really about mercury itself, why can't they explain why Japanese children don't suffer higher rates of autism even though they are exposed to much higher levels of mercury due to their diets which are heavy in seafood?

Well the simple answer is they really can't explain these questions, and they know it.  However to admit there is no such link between thimerosal and autism would mean the antivaxxers would need to admit they have been wrong all along - and we all know that isn't very likely.  The more complicated answer is that rather than admit thimerosal doesn't cause autism, most antivaxxers will attempt to switch gears and claim it was never about thimerosal but rather about all vaccines causing autism.  Don't bother asking for the science to support these theories however as they can't provide it.  

This is typically the point that the typical antivaxxer (Mr. Hubbs included) will start professing that the FDA or CDC or "Big Pharma" or some other agency or organization is suppressing the studies which would prove such a link, but aside from a conspiracy theorist it is hard to actually accept such an explanation.  There are countless scientific agencies, research hospitals, Universities, and private companies in American any of which is capable of performing such studies and proving a link if one exists - yet we are expected to believe that every one of the researchers, scientists, doctors, and other trained experts who work for these various organizations is somehow in bed with the drug companies so they are unwilling to produce a study which could possibly have a negative impact upon the financial stability of these companies?

I ask anyone with a rational mind if this seems even remotely plausible.  Aside from the fact it would be a sheer impossibility to pay off or otherwise silence tens of thousands of people without at least a few of them blowing the whistle, the fact is America doesn't control all scientific discovery on the planet.  There are dozens of nations out there doing their own research, and yet not a single one of these nations has ever produced a single study which has been able to prove a link between vaccines and autism.  

Does this sound like a coincidence?  Are we to believe there is some vast multi-national conspiracy to hide the truth from the other six billion humans on Earth who aren't somehow connected to the medical or scientific community?  Or could it possibly be that Mr. Hubbs and his compatriots are merely ignorant of scientific fact and unwilling to accept the truth?  I think the answer is more than obvious.

However, if anyone has any doubts about the safety or long-term impacts of thimerosal, there  have been a few studies performed on the subject which are readily available to review.  A word of caution however - if you are an antivaxxer, reading any of these studies is bound to make your head explode from all of the scientific research and fact, so don't say you weren't warned:

  1. Batts AH, Narriott C, Martin GP, et al. The effect of some preservatives used in nasal preparations on mucociliary clearance. Journal of Pharmacy and Pharmacology 1989; 41:156-159.
  2. Batty I, Harris E, Gasson A. Preservatives and biological reagents. Developments in Biological Standardization 1974;24:131-142.
  3. Beyer-Boon ME, Arntz PW, Kirk RS. A comparison of thimerosal and 50% alcohol as preservatives in urinary cytology. Journal of Clinical Pathology 1979;32:168-170.
  4. Gasset AR, Itoi M, Ishii Y, Ramer RM. Teratogenicities of ophthalmic drugs. II. Teratogenicites and tissue accumulation of thimerosal. Archives of Ophthalmology 1975;93:52-55.
  5. Goldman KN, Centifanta Y, Kaufman HF, et al. Prevention of surface bacterial contamination of donor corneas. Archives of Ophthalmology 1978;96:2277-2280.
  6. Keeven J, Wrobel S, Portoles M, et al. Evaluating the preservative effectiveness of RGP lens care solutions. Contact Lens Association of Ophthalmologists Journal 1995;21:238-241.
  7. Naito R, Itoh T, Hasegawa E, et al. Bronopol as a substitute for thimerosal. Developments in Biological Standardization 1974;24:39-48.
  8. Wozniak-Parnowska W, Krowczynski L. New approach to preserving eye drops. Pharmacy International 1981;2(4):91-94.

*Average for Chunk White Canned Tuna. Yess, Norma J. "US Food and Drug Administration Survey of Methyl Mercury in Canned Tuna," Journal of AOAC International, Vol. 76, No. 1, 1993, pp. 36-38. 

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