Thimerosal

Thimerosal (sometimes spelled as thimerosol and thiomersal[1]) (trade name: Merthiolate) is an organometallic compound used commonly since the 1930s as a preservative in some vaccines. Its chemical formula is C₉H₉HgNaO₂S. In the body it is metabolized to ethylmercury (C₂H₅Hg⁺) and thiosalicylate. Thimerosal has proven to be highly effective against bacterial contamination in multidose containers of vaccinations.[2] Thimerosal causes susceptible bacteria to autolyse, via an unknown mechanism.

Thimerosal controversy

Background for the controversy

Resistance to vaccination prorams first arose in 1853 and has remained active since, though with limited success. The thimerosal controversy is a recent addition to this long-standing debate.

In 1997, Frank Pallone, a United States congressional representative from New Jersey, included an amendment to an Food and Drug Administration (FDA) reauthorization bill requiring the agency to "compile a list of drugs and foods that contain intentionally introduced mercury compounds and … [to] provide a quantitative and qualitative analysis of the mercury compounds in the list…."

On December 14, 1998 and April 29, 1999, the FDA posted notice to vaccine manufacturers to supply information about the use of mercury in vaccines. Through its Center for Biologics Evaluation and Research (CBER), the FDA studied the results and found regularly vaccinated young children were injected with 187.5 μg of ethylmercury by the time they were six months old. When trying to assess whether this dosage was likely to cause damage, the CBER could not find guidelines for ethylmercury. Three federal agencies had published different safety guidelines on the common pollutant methylmercury. Without knowing whether ethylmercury was more or less toxic than methylmercury, they found the administered dosage exceeded the lowest guideline of those three published by the US agencies. All the guidelines had been set with a considerable margin of safety based on a study done on Iraqi children who had been exposed to methylmercury in utero.

From 1998 to 1999, the European Medicines Agency undertook a study of the effects of thimerosal, concluding "although there is no new evidence of harm caused by the level of exposure, it would be prudent to promote the general use of vaccines without thimerosal within the shortest possible time frame."

In June of 1999, Dr. Neal A. Halsey, the director of the Johns Hopkins University Institute for Vaccine Safety, and a vocal defender of vaccination policy, was apprised of the results of the CBER study and enlisted Dr. Walter Orenstein, the director of the Centers for Disease Control's (CDC) National Immunization Program to give advice. Along with leaders of the American Academy of Pediatrics (AAP), the group advised a cautious stance by informing physicians about the findings. Negotiations within the AAP resulted in a press release calling for a delay of Hepatitis B vaccines under certain circumstances.[3]

State of the controversy

Critics argue there there is evidence ([4] and [5], among others) thimerosal causes adverse effects among certain children, possibly being a contributing factor for autism or other neurological disorders. Mark Geier and his son David Geier have conducted several studies cited as evidence for banning the use of thimerosal. However, one of their papers was alleged to be flawed by the AAP. [6]

In a 2004 report, the United States National Academy of Science's (NAS) Institute of Medicine (IOM) concluded "this body of evidence favors rejection of a causal relationship between thimerosal-containing vaccines (TCVs) and autism, and that hypotheses generated to date concerning a biological mechanism for such causality are theoretical only." [7] Before the IOM released its final version of the report,[8] one influential researcher, whose work found "no consistent significant association" [9] between the preservative and neurodevelopmental outcomes, nevertheless wrote in a medical journal, "The bottom line is and has always been the same: an association between thimerosal and neurological outcomes could neither be confirmed nor refuted, and therefore, more study is required." [10] The research is still intensely debated. [11]

The US National Institute of Allergy and Infectious Diseases (NIAID) states, "Not much is known about the effects of thimerosal exposure on humans and how this compares to methylmercury exposure. The only known side-effects of receiving low doses of thimerosal in vaccines have been minor reactions such as redness and swelling at the injection site." [12]

The latest controversy surrounds a newly-released, NIH-funded primate study [13], [14], conducted by Dr. Thomas Burbacher,[15] an associate professor of environmental health and the director of the primate research center at the University of Washington. In his study, the effects of injected ethylmercury were compared with those of orally administered methylmercury in order to ascertain whether methylmercury provided a suitable reference for assessing the effects of ethylmercury found in thimerosal. The study revealed significant differences between methyl- and ethylmercury metabolism.

The injected ethylmercury cleared from the bloodstream much more rapidly than ingested methylmercury. However, the study also found that a larger fraction of the ethylmercury that remained in the primates' brains was converted to potentially more harmful inorganic compounds. Burbacher did not draw conclusions regarding the relative toxicity of ethylmercury versus methylmercury, but did warn that methylmercury is likely not a suitable reference for evaluating ethylmercury toxicity. In an interview, Burbacher commmented

"The bottom line is that trying to assess the effects of a compound with very little or no data is not a good thing to do. ... Unfortunately, we started doing studies on this compound way too late. Basic information like this should've been available decades ago."[16]

Autism advocacy groups (including Safe Minds, [17]) and United States Congressman Dave Weldon,[18] point out thimerosal was previously injected into children without sufficient understanding of its effects.

Public concerns about possible thimerosal toxicity have led to the production of many thimerosal-free vaccines as a precautionary measure to ensure vaccination is not rejected out of fear. In terms similar to the NIAID, the United States Centers for Disease Control and Prevention (CDC) states: "No harmful effects have been reported from thimerosal at doses used in vaccines, except for minor reactions"."[19] It further states: "Today, with the exception of some Influenza (flu) vaccines, none of the vaccines used in the U.S. to protect preschool children against 12 infectious diseases contain thimerosal as a preservative."

See also

• Autism epidemic
• Bernard Rimland
• Controversies in autism
• David Kirby
• Iatrogenesis
• Vaccine controversy

External links

• CDC.gov – 'Mercury and Vaccines', US Centers for Disease Control
• IOM.edu – Statement of Rep. Dave Weldon, M.D., Member of Congress, before the US Institute of Medicine, claiming a link between thimerosol and autism (February 9, 2004)
• JFPOnline.com – 'Reconnoitering the Antivaccination Web Sites: News From the Front', Laeth Nasir, MBBS, Journal of Family Practice (October, 2003)
• Merck.de – 'Thimerosal USP' (manufacturer's product info)
• MumsNet.com – 'Are the CDC, the FDA, and other health agencies covering up evidence that a mercury preservative in children's vaccines caused a rise in autism?', Andrea Rock (March/April 2004)
• News-Leader.com – Missouri: 'Senate votes to limit mercury in childhood vaccine', James Goodwin, Springfield News-Leader (May 12, 2005)
• OpinionJournal.com – 'Autism and vaccines: Activists wage a nasty campaign to silence scientists', editorial, Wall Street Journal (February 16, 2004)
• QuackWatch.org – Misconceptions about Immunization: 'Misconception #11, Thimerosal Causes Autism: Chelation Therapy Can Cure It'
• Science Daily – 'Vaccines Are Not Associated With Autism, Report Says' (May 19, 2004)
• SpikedOnline.com – 'Immune to the facts: Is the UK media to blame for the anti-MMR scare?', Dr. Michael Fitzpatrick (March 23, 2003)
• VaccineSafety.edu – 'In Vitro studies of pure thimerosal and vaccines with and without thimerosal added as a preservative: Comparison to Hg(II) toxicity', Testimony before the House Committe on Government Reform, Boyd E. Haley, (April 9, 2001)
• Weldon.House.gov (pdf) – Speech to Congress by Rep. Dave Weldon, M.D., on autism epidemic, claiming IOM report flawed (June 18, 2004)

References

• AAPPublications.org – 'Do Vaccines Contain Harmful Preservatives, Adjuvants, Additives, or Residuals?', Paul A. Offit, MD, Rita K. Jew, PharmD, Pediatrics, Vol 112, No 6, pp. 1394–1397, December, 2003
• AAPPublications.org – 'An Assessment of Thimerosal Use in Childhood Vaccines', Leslie K. Ball, MD, Robert Ball, MD, MPH, and R. Douglas Pratt, MD, MPH, Pediatrics Vol 107, No 5, May 2001, pp. 1147–1154
• AAPPublications.org – 'Thimerosal and the Occurrence of Autism: Negative Ecological Evidence From Danish Population-Based Data', Kreesten M. Madsen, MD, Marlene B. Lauritsen, MD, Carsten B. Pedersen, Msc, Poul Thorsen, MD, PhD, Anne-Marie Plesner, MD, PhD, Peter H. Andersen, MD and Preben B. Mortensen, MD, DMSc, Pediatrics Vol 112, No 3, September 2003, pp. 604–606
• AAPPublications.org – 'Safety of Thimerosal-Containing Vaccines: A Two-Phased Study of Computerized Health Maintenance Organization Databases', Thomas Verstraeten, Robert L Davis et al, Pediatrics Vol 112, No 5, November 2003, pp 1039–1048
• AAPPublications.org – 'Thimerosal, the Centers for Disease Control and Prevention, and GlaxoSmithKline', Thomas Verstraeten, Pediatrics, Vol 113 No 4, April 2004, pp. 932.
• JPandS.org – 'Thimerosal in Childhood Vaccines, Neurodevelopment Disorders and Heart Disease in the United States' Mark and David Geier, Journal of American Physicians and Surgeons, Vol 8, No 1, Spring, 2003