The Scientific Review of Alternative Medicine

And Aberrant Medical Practices

Mercury in vaccines as a cause of autism and Autism Spectrum Disorders (ASDs): A failed hypothesis

Author: David Gorski

Introduction: Mercury, Celebrities and Misrepresenting Science

One of the most pernicious medical myths of recent years has been the claim, promulgated by a subgroup of parents of autistic children and facilitated by scientists of dubious repute, that the mercury in the thimerosal (ethyl mercury) preservative used in common childhood vaccines in the U.S. until early 2002 causes autism. Although it had been percolating under the radar of most parents and scientists for several years before, this belief invaded the national zeitgeist in a big way in 2005, beginning with the publication of a book by journalist David Kirby entitled Evidence of Harm: Mercury in Vaccines and the Autism Epidemic: A Medical Controversy.1 The fires of hysteria were fanned by Robert F. Kennedy Jr., who, in June of that year, published a piece simultaneously in Rolling Stone and on Salon.com entitled Deadly Immunity.2 Selectively quoting the transcript of a conference held by the CDC3 and an Institute of Medicine report on vaccines,4 while simultaneously misrepresenting the results of an early draft and the eventual finished paper by Verstaeten et al5,6 to paint a false picture of a government coverup, RFK Jr. managed to stoke fears that vaccines were causing an “epidemic of autism.”7,8,9,10

RFK Jr., unfortunately, had help. Relying on the dubious research of investigators such as the father-and-son team of Dr. Mark Geier and David Geier—whose prodigious output of badly designed studies11 emanating from a lab in their home in suburban Maryland, done using a rubber-stamp institutional review board12 stacked with cronies to approve the studies, and published for the most part in non-peer-reviewed journals—activists insisted that mercury in vaccines was the cause of most cases of autism.13 Others claiming to demonstrate this link include Boyd Haley, a chemist from the University of Kentucky, and a few other vocal scientists and advocates, who claim that autism is, in essence, mercury poisoning.14 Facilitating the dissemination of this message were reporters such as David Kirby and media personalities such as Don Imus. Indeed, some activists claimed that some vaccines were “poisoning” our children, even going so far as to show photos of autistic children with the label “mercury-poisoned?”15 underneath them on placards held aloft at protest rallies. The placards made quite a splash then, and still do even today.

There’s just one problem. The scientific data, taken in totality, do not support a link between mercury in vaccines and autism. An important study by Robert Schechter and Judith Grether was recently published in the Archives of General Psychiatry entitled Continuing Increases in Autism Reported to California’s Developmental Services System: Mercury in Retrograde16 that failed to support the hypothesis that mercury in vaccines is an etiological factor in autism. It is yet another nail in the coffin of the medical myth that mercury in vaccines causes autism.

Background

In response to the FDA Modernization Act of 1997—and prior to the hypothesis that thimerosal might cause autism—the U.S. Food and Drug Administration (FDA) compiled a list of vaccines and how much thimerosal they contained. Thimerosal had been commonly used to prevent microbial contamination of vaccines, particularly multidose vials, since the 1930s. It could be argued, given the more lax standards of the time, that thimerosal had not been adequately tested before use in humans; yet decades of use after that had, as far as could be discerned, revealed only occasional skin hypersensitivity reactions due to this component. By 1999, parent groups and some scientists, including Dr. Neal Halsey, the head of the American Academy of Pediatrics’ vaccine advisory expressed concern that infants before six months of age were potentially being exposed to cumulative doses of ethyl mercury that may have exceeded safety standards.17 These safety standards were based on an indirect surrogate of ethyl mercury, namely methyl mercury, and largely in the absence of real data. In July, 1999, largely due to Dr. Halsey’s advocacy (or, as Dr. Offit described it in his recent book, bullying17), the American Academy of Pediatrics (AAP) and the U.S. Public Health Service (PHS) decided, as a precaution, to recommend that thimerosal be removed as soon as possible from childhood vaccines.18

It did not take long for this recommendation to be implemented. By March, 2001, all vaccines in the recommended infant vaccination schedule were available in forms that had very little or no thimerosal left over from the manufacturing process. The last lots of childhood vaccines containing thimerosal had expiration dates in 2002. Indeed, as journalist Arthur Allen documented in his recent book Vaccine: The Controversial Story of Medicine’s Greatest Lifesaver,?? a survey of several hundred medical offices conducted in February, 2002 by the CDC found that of the three pediatric vaccines that contained thimerosal in the 1990s, only 2% of vaccine stock still contained thimerosal. Since then, with the exception of the flu vaccine, no childhood vaccine in the U.S. has contained more than trace amounts of thimerosal.

There has been considerable debate over whether the decision to remove thimerosal was undertaken too quickly. At the time it seemed like a prudent, cautious step. But the decision had unintended consequences. One was that it resulted in a temporary shortage of childhood vaccines. More importantly, it fed the fears of activists that the mercury in vaccines is actually harmful. After all, if it weren’t harmful, why would the AAP and PHS recommend its removal?

Why indeed? The use of this precautionary measure as justification for attacking the safety of vaccines is a good example of how no good deed goes unpunished. Many parents, faced with the enormous challenge of raising children with autism, reasonably wondered whether there was something wrong with vaccines in the first place.

More pertinent background information is that, over the last couple of decades, the incidence of autism and autism spectrum disorder (ASD) has increased markedly: Before 1990, its prevalence in America was 4.7 per 10,000; now it’s 60 per 10,000. Robert F. Kennedy Jr. and others who believe that mercury in vaccines causes autism have referred to this increase as an “autism epidemic” (or, more offensively, as an “autism tsunami”20) and claim that an environmental factor must have caused the increase. Because the symptoms of autism, such as cognitive delay and withdrawal from interaction with parents, often manifest themselves between one and three years of age, and because this is the age when children receive the bulk of their vaccines, there is a correlation. However, correlation does not necessarily equal causation. Often the correlation is spurious, unrelated, or related to a common factor. More investigation is always required to determine if an apparent correlation is or is not due to causation. In the case of autism, there is good evidence, most recently published by Paul Shattuck,21 that increased awareness and diagnostic substitution (the criteria for a diagnosis of ASD were broadened in 1994) account for the apparent increase in cases of autism.22,23,24

Reality Testing: Denmark and Canada

Regarding the question of vaccines and autism, for ethical reasons we cannot do a double-blind, randomized, controlled trial of vaccines with and without thimerosal. We can do the next best thing, however, and several good studies have been published since 1999 that do just that. Some of these studies are epidemiological; some are ecological. What allows us to use them to reject the hypothesis that mercury in vaccines is an etiological agent? Quite simply, if the hypothesis were true, then we would expect that the removal of thimerosal from vaccines would lead to a rapid decrease in autism incidence and prevalence within two to five years.

There have now been several studies that have examined this hypothesis in countries that removed thimerosal from their vaccines before the U.S. did. In Denmark, for example, Hviid and colleagues25 reported that autism prevalence increased from 1991 to 1996 despite the removal of thimerosal from vaccines. In a separate study, Madsen and colleagues26 looked at the time period from 1971 to 2000 and concluded that autism diagnoses continued to increase after thimerosal was removed from vaccines. Neither study supported a causal link between thimerosal-containing vaccines (TCVs) and autism, and they were a prominent part of the dataset that was used by the Institute of Medicine to conclude, in 2004, that no good evidence supports a link between TCVs and autism.27

A more recent study by Fombonne and colleagues in Montreal examined 27,749 children born from 1987 to 1998 attending 55 different schools.28 Cumulative thimerosal exposure by age 2 years was calculated for the 1987 to 1998 birth cohorts. This exposure ranged from 100-125 íg from 1987 to 1991, 200-225 íg from 1992 to 1995, and then none after 1996, which was when thimerosal was completely removed from vaccines in Canada. Their findings: autism, ASD, and pervasive developmental disorder diagnoses continued to increase in all periods, demonstrating no relationship between TCVs and autism or ASDs. Even more recently, a large study failed to support a relationship between thimerosal and adverse neurodevelopmental outcomes.29 One of the investigators in the study, Sallie Bernard, a proponent of the thimerosal hypothesis, took the unusual step of criticizing the study in essence because it did not show what she had hoped that it would show,30 despite the fact that she had been involved in its design.

Reality Testing: California

Nearly seven years have passed since the near-complete removal of thimerosal from vaccines in the U.S. Other than the flu vaccine, there is no more than trace thimerosal in any childhood vaccine; overall mercury exposure due to vaccines has not been this low in decades. Consequently this hypothesis can now be tested in the United States. In an ironic twist, in their study refuting the mercury hypothesis Schechter and Grether16 used a source of data—the California Department of Developmental Services (CDDS) database31—that has frequently been abused by advocates to try to show a link between TCVs and autism where there isn’t one.32,33,34 The CDDS database has even been referred to as the “gold standard” of autism epidemiology (although it probably is not) by activist David Kirby.35 Kirby predicted that there should be a noticeable decrease in new diagnoses of autism in this database by 2007 if the thimerosal hypothesis were true,36 but later shifted the goalposts to 2011 when it became apparent that there had been no decrease.37

The CDDS administers a statewide system of regional centers and developmental centers designed to serve people who are substantially disabled because of autism, mental retardation, or other developmental disabilities. It maintains an archive file of “client developmental evaluation reports” (CDER). Among its strengths is that it is a population-based system representing the most populous state in the U.S. Moreover, the client reporting form was consistent throughout the study period, preventing confounders due to changes in reporting. A weakness is that the data are derived from an administrative system that was designed to track enrollment and fiscal data; as such, they are not as well suited to measuring the occurrence of developmental disabilities in the population. With proper statistical analysis, however, considerable information can be gleaned from these data for specific birth cohorts.

In order to ask the question of whether autism rates had declined, Schechter and Grether16 examined data reported from January 1, 1995 to March 31, 2007. Using careful statistical analyses, they used two approaches to measure the occurrence of ASD during this period. The second approach, in which ASD prevalence was determined in the 3 to 5-year-old cohort, is the more informative. It shows a continuing increase in autism prevalence without even a blip or decrease in the rate of increase after 2002. This result is not only consistent with multiple other published and unpublished studies,38 including the aforementioned Danish and Canadian studies, but it is about as unambiguous evidence as can be obtained from the CDDS database.

Hoisted by their own Petard

Despite the limitations of the use of this database, it is an excellent example of proponents of the “mercury injury” hypothesis of autism being “hoisted by their own petard,” so to speak. Eric Fombonne, in an editorial accompanying Schechter and Grether’s paper, agrees:

The particular significance of the study by Schechter and Grether is that it relies on the California Department of Developmental Services database, which has been systematically used by proponents of the thimerosal hypothesis to argue that the rising number of children accessing these services—or the “epidemic” of autism—was linked to the increasing exposure to ethyl mercury of U.S. children occurring in the 1990s through the changes in the immunization schedule. To the contrary, the data analyzed by Schechter and Grether provide a clear and unambiguous test that shows that the expected decline in autism rates following discontinuation of thimerosal in U.S. vaccines did not occur.39

Noting that, “with the exception of studies conducted by a single pair of authors” (Fombonne does not name whom he must have meant: Mark and David Geier), all studies done have thus far failed to find a link between TCVs and autism. Fombonne continues:

Despite the accumulation of scientific evidence rejecting these two hypotheses linking autism to various components of childhood vaccines, these theories and the practices that accompany them have not faded away. Why? How many more negative study results are required for the belief to go away, and how much more spending of public funds on this issue could even be justified?39

He then postulates an explanation with which I agree:

Outside academic circles, powerful advocacy groups developed and started to lobby decision makers to influence decisions about which autism research to fund and even how to conduct it. Unaware of scientific studies, or worse, doubtful of their results, bestselling writers, journalists, and politicians were drawn to embrace conspiracy theories that portrayed vaccine manufacturers and the Centers for Disease Control and Prevention as public enemies. Law firms saw an opportunity to obtain large financial compensations from the U.S. Vaccine Injury Compensation Court or before local federal courts, the viscous U.S. legal process allowing for fermentation of misconceptions. Exploiting further families’ beliefs and their understandable desire to try everything possible to help their children, charlatans developed alternative (and lucrative) “treatments” for autism, which included chelation therapy, use of a hyperbaric oxygen chamber, and testosterone suppression. All are of unproven efficacy, and many are dangerous.39

In other words, it’s all about obtaining compensation and “biomedical treatments” for this nonexistent “vaccine injury.” Never mind that these “treatments” are neither scientifically plausible nor have convincing evidence in the form of well-designed clinical trials to support their efficacy in ameliorating the cognitive delays observed in autistic children. Unfortunately, parents who love their autistic children and desperately want to do something to “make them better” are fertile ground for the blandishments of proponents of these implausible and unproven “therapies.” Some of these treatments, such as chelation therapy—which, it is claimed, will remove the mercury that is purportedly the root cause of autism—have developed into cottage industries that prey on desperate parents. This has resulted in the death of at least one child, a 5-year-old boy.40

It has even progressed to the point where the Geiers can convince some parents that most autistic children exhibit signs of “precocious puberty” and that the elevated testosterone in such children forms “sheets” that bind mercury and prevent it from being chelated properly.41 As hard as it is to believe, they then use that claim as a justification for using powerful anti-androgenic drugs such as Lupron on autistic children to treat their autism.

Comment

Vaccination is the most effective public health intervention ever developed. As recently as 50 years ago, our parents and grandparents lived in deathly fear of diseases like polio, which has since been virtually eradicated. Because they are preventative in nature and administered to a very large population of healthy people, vaccines have a very high hurdle to jump as far as safety is concerned: when an intervention is performed on millions of otherwise healthy people, even a low rate of complications can result in large numbers of injured people. Modern vaccines have achieved that level of safety. Are they completely safe? Nothing in medicine is 100% safe. In comparison to the risks of the diseases they prevent and by any reasonable standard, the risks due to modern vaccines are extremely low. Moreover, the claims of proponents of an increasingly untenable hypothesis to the contrary, there is no convincing evidence that TCVs, or vaccines in general, have anything to do with the etiology of autism. Whatever tiny risk there may be from childhood vaccines, autism and ASDs are not among them.

Even before the study by Schechter and Grether, under the onslaught of studies that all failed to find a link between thimerosal and autism, David Kirby and others were starting to back away from the hypothesis, invoking vague “environmental toxins” or going so far as to blame mercury from pollution wafting over from China or, even more ludicrously, mercury from the cremation of bodies with mercury amalgam dental fillings.42 In the wake of the study, activist Mark Blaxill retreated to claiming that “the epidemiological analysis doesn’t prove that thimerosal exposure cannot cause individual cases of autism” and blaming vaccines in general for autism.43

The Schechter and Grether study is clearly but one more nail in the coffin of this dying hypothesis. Unfortunately, like Jason in the Friday the 13th movies, the hypothesis that mercury in vaccines is a major cause of autism just refuses to die, no matter how many studies fail to find even a wisp of a link between the two. That’s why it is not difficult to predict that the usual suspects will refuse to believe it, just as they have refused to believe the studies preceding it.

References

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  2. Kennedy Jr. RF. Deadly Immunity. Slate. 2005. Accessed 12/08 at: http://dir.salon.com/story/news/feature/2005/06/16/thimerosal/.
  3. Center for Disease Control. Scientific Review of Vaccine Safety Datalink Information. Simpsonwood Retreat Center: Norcross, Georgia; 2000. Accessed 10/08 at: http://www.safeminds.org/legislation/foia/Simpsonwood_Transcript.pdf.
  4. National Academy of Sciences Institute of Medicine. Organizational meeting of Immunization Safety Review Committee (Closed Session); Jan. 12, 2001. Accessed 10/08 at: http://www.nomercury.org/iom/iom.pdf.
  5. Verstraeten T, Davis R, DeStefano F et al. Risk of neurologic and renal impairment associated with thimerosal-containing vaccines. Draft dated June 1, 2000. Accessed 10/08 at: http://safeminds.org/legislation/foia/VSD_VerstraetenJune2000.pdf.
  6. Verstraeten T, Davis RL, DeStefano F, et al. Safety of thimerosal-containing vaccines: a two-phased study of computerized health maintenance organization databases. Pediatrics 2003;112:1039–1048.
  7. From the vaults: RFK, Jr. gets his first taste ever of Respectful Insolence.ª Respectful Insolence weblog. June 20, 2006. Accessed 10/08 at: http://scienceblogs.com/insolence/2006/06/from_the_vaults_rfk_jr_gets_hi.php.
  8. Robert F. Kennedy Jr.’s completely dishonest thimerosal article. Skeptico weblog. June 20, 2005. Accessed 10/08 at: http://skeptico.blogs.com/skeptico/2005/06/robert_f_kenned.html.
  9. Lies, Damn Lies, and Quote-Mining. Skeptico weblog. June 29, 2005. Accessed 10/08 at: http://skeptico.blogs.com/skeptico/2005/06/lies_damn_lies_.html.
  10. The Verstraeten et al Gambit. Natural Variation-Autism weblog. Nov. 20, 2006. Accessed 10/08 at: http://autismnaturalvariation.blogspot.com/2006/11/verstraeten-et-al-gambit.html.
  11. The Geiers go Dumpster-Diving Yet Again. Respectful Insolence weblog. Mar 6, 2006. Accessed 10/08 at: http://scienceblogs.com/insolence/2006/03/the_geiers_go_dumpsterdiving_y_1.php.
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  13. Seidel K. Too Daunting a Hurdle to Scale. Neurodiversity weblog. Dec. 30, 2007. Accessed 10/08 at: http://neurodiversity.com/weblog/article/140/.
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  16. Schechter R and JK Grether. Continuing Increases in Autism Reported to California’s Developmental Services System. Arch. Gen. Psychiatry 2008; 65: 19–24.
  17. Offit PA. Autism’s False Prophets: Bad Science, Risky Medicine, and the Search for a Cure. New York: Columbia University Press; 2008.
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  27. Institute of Medicine of the National Academy of Sciences. Immunization Safety Review: Vaccines and Autism. May 17, 2004. Available at: http://www.iom.edu/CMS/3793/4705/20155.aspx.
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  30. Press Release: Vaccine Study In New England Journal Of Medicine Wrong In Concluding Mercury Exposures Are Harmless, States Safeminds. SafeMinds website. Sept. 26, 2007. Accessed 10/08 at: http://www.safeminds.org/pressroom/vaccine-study.html.
  31. State of California Department of Developmental Services. Diagnostic Information and Instruments. Accessed 10/08 at: http://www.dds.cahwnet.gov/FactsStats/Diagnostic_Main.cfm.
  32. A Review of “Early Downward Trends in Neurodevelopmental Disorders Following Removal of Thimerosal-Containing Vaccines.” Interverbal: Review of Autism Statements and Research weblog. March 15, 2006. Accessed 10/08 at: http://interverbal.blogspot.com/2006/03/review-of-early-downward-trends-in_15.html.
  33. CDDS Data 101. Natural Variation-Autism weblog. Mar 2, 2006. Accessed 10/08 at: http://autismnaturalvariation.blogspot.com/2006/03/cdds-data-101.html.
  34. The demise of the thimerosal hype. Autism Diva weblog. Jan 12, 2007. Accessed 10/08 at: http://autismdiva.blogspot.com/2007/01/demise-of-thimerosal-hype.html.
  35. Kirby D. Autism, Mercury, and the California Numbers. Huffington Post. July 13, 2005. Accessed 10/08 at: http://www.huffingtonpost.com/david-kirby/autism-mercury-and-the-c_b_4133.html.
  36. Kirby D. Email to Citizen Kane. Reported in: Slouching Toward Truth–Autism and Mercury. Citizen Kane weblog. Nov 30, 2005. Accessed 10/08 at: http://citizencain.blogspot.com/2005/11/slouching-toward-truth-autism-and_30.html.
  37. Kirby D. The Autism-Vaccine Debate: Anything but Over. Huffington Post. Nov 30, 2007. Accessed 10/08 at: http://www.huffingtonpost.com/david-kirby/the-autismvaccine-debate_b_74853.html.
  38. Parker SK, B Schwartz, J Todd, and LK Pickering. Thimerosal-containing vaccines and autistic spectrum disorder: a critical review of published original data. Pediatrics 2004; 114:793–804.
  39. Fombonne E. Thimerosal disappears but autism remains. Arch. Gen. Psychiatry 2008; 65: 15–16.
  40. Commonwealth of Pennsylvania Bureau of Professional and Occupational Affairs vs. Roy Eugene Kerry, MD, Respondent. September 8, 2006. Accessed 10/08 at: http://www.circare.org/pd/kerry_ordertoshowcause_20060908.pdf.
  41. Seidel K. Significant Misrepresentations: Mark Geier, David Geier & the Evolution of the Lupron Protocol (contents). August 25, 2006. Neurodiversity weblog. Accessed 10/08 at: http://neurodiversity.com/weblog/article/109/.
  42. Allen A. A story with legs. Jan 18, 2007. Vaccine the Book website. Accessed 10/08 at: http://vaccinethebook.typepad.com/mt/2007/01/a_story_with_le.html.
  43. Blaxill M. Making sense of the California autism numbers. Jan 6, 2008. Age of Autism website. Accessed 10/08 at http://www.ageofautism.com/2008/01/making-sense—1.html.

About the Author

David H. Gorski, MD, PhD, Program Leader, Breast Cancer Biology Program, Barbara Ann Karmanos Cancer Institute; and Associate Professor of Surgery, Wayne State University School of Medicine. Please send e-mail correspondence to gorskid@med.wayne.edu, or mail to 4100 John R St Mailcode HW08A0, Detroit, MI 4820.

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