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Revision as of 18:38, 31 January 2007

In recent years, it has been suggested that thimerosal in childhood vaccines could contribute to, or cause, a range of neurodevelopmental disorders in children, most notably autism and related Pervasive Developmental Disorders (PDDs), or other cognitive disorders, including Attention Deficit Hyperactivity Disorder (ADHD). Critics of vaccines containing thiomersal argue that the ethylmercury-based preservative may cause serious side effects, especially when administered to young children who have relatively undeveloped immune and neurological systems that may be seriously affected.

There is concern on both sides of the debate in regards to motivating factors. Those who denounce thimerosal suspect that government agencies and pharmaceutical companies are denying a connection for fear of financial liability and the creation of mistrust in vaccinations. Those who deny a connection between thimerosal and neurological disorders have charged thimerosal's critics as being medically and scientifically unqualified, emotionally distraught, or interested in pursuing litigation.

Basis for concerns

The Food and Drug Administration (FDA) Modernization Act of 1997 called for a review and risk assessment of all mercury-containing food and drugs. Vaccine manufacturers responded to FDA requests for December 1998 and April 1999 to provide detailed information about the thimerosal content of their preparations. From the early 1970s until present day, the number of vaccines regularly received by children in the US before the age of four has risen from two or three to up to twenty-two.

Through its Center for Biologics Evaluation and Research (CBER), the FDA studied the results and found regularly vaccinated young children were injected with up to 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.

The FDA recognized that some children who receive thimerosal-containing vaccines may have, over time, exceeded federal guidelines for bolus (single-dose) mercury exposure, based on methylmercury (but not ethylmercury) studies. The United States Public Health Service (PHS), American Academy of Pediatrics (AAP) and vaccine manufacturers agreed that thimerosal-containing vaccines should be removed as soon as possible because of the potential risk of adverse effects from mercury exposure. Similar conclusions were reached by the European Medicines Agency.

In June of 1999, Dr. Neal A. Halsey, director of the Johns Hopkins University Institute for Vaccine Safety, Former Chairman of the American Academy of Pediatrics and a vocal supporter of the vaccination policy, was apprised of the results of the CBER study. Dr. Halsey enlisted Dr. Walter Orenstein, the director of the Centers for Disease Control's (CDC) National Immunization Program for advice. Along with leaders of the American Academy of Pediatrics, 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.

Due to the concerns that were raised, the Centers for Disease Control and the National Institutes of Health (NIH) asked the National Academy of Science's (NAS) Institute of Medicine (IOM) to establish an independent expert committee to review hypotheses about existing and emerging immunization safety concerns. In 2001 the IOM committee concluded that the hypothesis was biologically plausible; however, the evidence was inadequate to accept or reject a causal relationship between thimerosal exposures from childhood vaccines and neurodevelopmental disorders.

The IOM panel reconvened in 2004 and concluded the evidence that was presented favored a rejection of a causal relationship between thimerosal-containing vaccines and autism; and that hypotheses generated to date concerning a biological mechanism for such causality are theoretical only. The IOM went on to recommend the termination of additional research into the subject, stating clearly that, "Further research to find the cause of autism should be directed toward other lines of inquiry". The IOM committee chair stated, "Available funding for autism research should be channeled to the most promising areas, of which the link with vaccines does not appear to be one."

Some advocacy groups felt the IOM's 2004 decision was premature.

The Journal of American Physicians and Surgeons (vol 11, no 1, Spring 2006), formerly the Medical Sentinel (a journal not listed in the major journal databases of PubMed and Web-of-Science), voice of the conservative Association of American Physicians and Surgeons, published a study indicating a corresponding downward trend for neurological disorders in children matching the decline of Thimerosal use in vaccines,. This article was followed by an article in The Medical Science Monitor "An assessment of downward trends in neurodevelopmental disorders in the United States following removal of thimerosal from childhood vaccines", a journal which is listed in the major journal databases of PubMed.

In an article "Mental Health in the United States: Parental Report of Diagnosed Autism in Children Aged 4--17 Years --- United States, 2003--2004" which was published in MMWR May 5, 2006/55(17);481-486., however, the CDC states:

"Finally, the findings in this report represent cross-sectional analyses of NHIS and NSCH data from interviews conducted during the same approximate period and do not assess trends in the rate of autism."

A report prepared by staff of the Subcommittee on Human Rights and Wellness, Committee on Government Reform, United States House of Representatives was published in The Congressional Record of May 21, 2003, detailing the results of its own investigation. It concluded:

"...However, the Committee, upon a thorough review of the scientific literature and internal documents from government and industry, did find evidence that thimerosal did pose a risk.
Thimerosal used as a preservative in vaccines in likely related to the autism epidemic. This epidemic in all probability may have been prevented or curtailed had the FDA not been asleep at the switch regarding the lack of safety data regarding injected thimerosal and the sharp rise of infant exposure to this known neurotoxin. Our public health agencies’ failure to act is indicative of institutional malfeasance for self-protection and misplaced protectionism of the pharmaceutical industry"

Vaccines with "trace" amounts of Thimerosal

Today, discussions or descriptions of vaccines frequently include comments to the effect that the subject vaccine does not contain thimerosal as a preservative. It should be noted that this does not mean that the vaccine is absolutely free from, but that some may include thimerosal in "trace" amounts. Criteria for what "trace" actually means appears to vary - one common definition describes a "trace" amount as being 1 microgram of mercury per dose or less.

The actual amount of thimerosal present in vaccines currently listed on the childhood vaccination schedule, whether trace or otherwise, varies from nil to 0.01%.

Other products that may contain thimerosal include products derived from blood plasma such as Rho(D) Immune Globulin, pit viper antivenin and coral snake antivenin, as well as black widow spider antivenin.

Differing effects of ethylmercury in Thimerosal containing vaccines

NIH funded a primate study, conducted by Dr. Thomas Burbacher an associate professor of environmental health and the director of the primate research center at the University of Washington. 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 said, "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.".

State of the controversy

Below are some of the arguments raised against including thiomersal in vaccines:

  • Appeal for caution: injecting an organic mercury compound into small childrens' tissues and bloodstream has the potential to cause harm.
  • In vitro tests to examine the effects of ethylmercury on living cells show normal effects on these cells
  • In vivo test on lab animals show wide range of adverse effects
  • Mass data analysis of actual populations to discern patterns, ideally with a control group. This includes study of the incidence of autism in populations with varying use of thimerosal.
  • Clinical studies comparing autistic and neurotypical children's reactions to mercury excretion
  • Trend analysis following introduction of more vaccines with thimerosal and the gradual abolishment of thimerosal in vaccines, starting a few years ago.
  • Thiomersal is unnecessary for the immunological purpose of vaccination.

Thimerosal is used in multi-dose vaccine vials in effort to reduce the likelihood of microbial contamination. The need for bacteriostatic agents like thimerosal can be avoided by using a single dose vial. Packaging as single-dose vials increases the cost of manufacturing, shipping, storing, and delivering vaccines and is blamed, at least in part, for intermittent shortages of vaccines in recent years.

It has been assumed thimerosal has been removed from vaccines since 1999. However, some pharmaceutical companies did not receive regulatory approval for their thimerosal-free infant vaccines until 2003. Infant vaccines produced before 2003 may contain up to 25μg of thimerosal. These vaccines have not been recalled and it is possible they are still in use. They will not expire until 2006 at the earliest, 2008 at the latest. Currently the adolescent and adult tetanus vaccine and certain influenza vaccines still contain thimerosal.

Legal aspect to the controversy in the United States

In 1986, the National Childhood Vaccine Injury Act established a no-fault system for litigating claims against vaccine manufacturers. Under this law, all claims against vaccine manufacturers could not be heard in state or federal court, but had to be heard rather in the U.S. Court of Federal Claims (USCFC). This court, often referred to as the “vaccine court,” hears cases without juries and awards damages that typically are far below damage awards rendered in other courts. The damage amounts are often insufficient to compensate severely injured children.

In 2001, Dr Thomas Verstraeten, presented preliminary research for the Centers for Disease Control and Prevention in which he reported that calculations suggested that thiomersal may be linked to increased rates of autism. However, he made clear that the link was tenuous and required confirmation. Since that announcement, over 4,000 law suits have been filed by the parents and guardians of children whom they allege were affected by thimerosal. These have been grouped in what is called the Autism Omnibus Action before the vaccine court. A hearing is expected in June 2007.

In March of 2006, the U.S. 5th Circuit Court of Appeals ruled that plaintiffs suing three manufacturers of thiomersal could bypass the USCFC and litigate in either state or federal court using the ordinary channels for recovery in tort. Holder v. Abbott Laboratories Inc., 444 F.3d 383. The ruling is significant since this is the first time a federal appeals court has held that a suit of this nature may bypass the USCFC. The 5th circuit court reached its conclusion by first looking to the statutory intent of the 1986 National Childhood Vaccine Injury Act and determining that the intent of the statute was to protect the manufacturers of vaccines. In this case, Plaintiffs argued that thiomersal is not a vaccine, but a preservative and, therefore, the manufacturers cannot share in the protection afforded by the no-fault regime of the National Childhood Vaccine Injury Act.

See also

External links

Links to news sites or weblogs that have an interest in the thimerosal controversy. The list is broken into two groups, those that espouse the theory that thimerosal causes neurological disorders and those that reject the theory as unlikely.

News item

Accept theory

Science Institute of Medicine

Reject theory

References

  1. (undisclosed author) (2005-07-18). "Thimerosal in Vaccines". at thimerosal-lawsuits.com, possibly linked to autism99.org. Retrieved 2006-04-01. {{cite web}}: |author= has generic name (help); External link in |publisher= (help)CS1 maint: year (link) Extraction of information from FDA site plus additional information & discussion
  2. >Food and Drug Administration (2005-09-06). "Thimerosal in Vaccines". Retrieved 2006-04-01.{{cite web}}: CS1 maint: year (link)
  3. United States Court of Federal Claims (2002–2005). "Docket of Omnibus Autism Proceeding". {{cite web}}: Unknown parameter |accessdate or accessyear= ignored (help)CS1 maint: date format (link) Proceedings of ongoing claim in Washington DC, USA
  4. Michael Fumento (2005-06-30). "Fear Mongering over Childhood Vaccinations". Scripps Howard News Service. Retrieved 2006-04-01.{{cite web}}: CS1 maint: year (link)
  5. "NY Times Article Misrepresents Facts In Autism Mercury Link Cover-up". UnInformed Consent. 2005-08-08. Retrieved 2006-04-01.{{cite web}}: CS1 maint: year (link)
  6. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4826a3.htm
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  9. Halsey NA (1999). "Limiting infant exposure to thimerosal in vaccines and other sources of mercury". JAMA. 282 (18): 1763–6. PMID 10568650 Scanned copy.
  10. http://jama.ama-assn.org/cgi/content/full/282/18/1763
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  24. Thimerosal in Vaccines - US FDA
  25. Thimerosal Content of Vaccines Routinely Recommended for Children 6 Years of Age and Younger
  26. Mercury in Plasma-Derived Products - US FDA
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