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Thimerosal controversy
Thimerosal controversyIn recent years, it has been suggested that thimerosalin childhood vaccines could contribute to or cause neurodevelopmentaldisorders in children (most notably autism, but also other disorders on the PDDspectrum, such as ADHD). The basis for this claim is the introduction of an organic mercury compound — ethylmercury — straight into the tissueof young children. Some opponents of the use of thimerosal argue that this could have an effect on young children, who may have undeveloped immuneand neurological systemsthat would be affected in some way. 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. [1][2][3][4] Those who deny a connection between thimerosal and neurological disorders have charged thimerosal's critics as being medically and scientifically unqualified, [5][6]emotionally distraught, or interested in pursuing litigation. The Food and Drug Administration(FDA) Modernization Act of 1997 called for a review and risk assessment of all mercury-containing food and drugs. [7] 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 µgof 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.[8]Similar conclusions were reached by the European Medicines Agency. [9] In June of 1999, Dr. Neal A. Halsey, director of the Johns Hopkins UniversityInstitute 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. [10]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 [11]. Negotiations within the AAP resulted in a press release calling for a delay of Hepatitis B vaccines under certain circumstances.[12] 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 committeeto review hypotheses about existing and emerging immunization safety concerns. In 2001the 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. [13][14][15][16] The IOM panel reconvened in 2004and 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 terminationof 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." [17][18] Some advocacy groups felt the IOM's 2004 decision was premature. [19][20] State of the controversyBelow are some of the arguments raised by critics of thimerosal containing vaccines:
Critics point out that thimerosal is unnecessary for the immunologicalpurpose of vaccination. Thimerosal is used in multi-dose vaccine vials in effort to reduce the likelihood of microbialcontamination. The need for bacteriostaticagents like thimerosal can be avoided by using a single dose vial. 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. [41] It has been assumed thimerosal has been removed from vaccines since 1999. However, some pharmaceutical companies did not receive regulatoryapproval for their thimerosal-free infant vaccines until 2003. Infant vaccines produced before 2003 may contain up to 25?g 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. [42][43]Currently the adolescent and adult tetanus vaccine and certain influenza vaccines still contain thimerosal. For more information about the thimerosal controversy see links section below. See also
External links
Thimerosal related news and opinionsLinks 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. Accept theory
Reject theory
Categories: Vaccines| Autism
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