Immunizations: Misconception #11

May 27, 2011

A few physicians have been promoting the idea that the mercury content of vaccines is a cause of autism and that autistic children should undergo chelation therapy to be detoxified. Lawsuits have been filed, and several attorneys are advertising on the Internet for more clients. The situation arose because until recently, certain vaccines contained thimerosal, a mercury-containing preservative that is no longer used in most of the vaccines now recommended for children. However, there are several reasons why concerns about the use of thimerosal in vaccines are misguided:

  • The amounts of mercury involved were very small.
  • No link between mercury and autism has been proven. If the thimerosal in vaccines caused mercury poisoning, the symptoms would affect all parts of the nervous system.
  • Autistic children do not have the movement disorders and peripheral nerve damage that that are characteristic of mercury poisoning.
  • There is no scientific evidence or logical reason to believe that autism has a toxic cause.

Thimerosal has been used as preservative in biologics and vaccines since the 1930s because it prevents bacterial and fungal contamination, particularly in multidose containers. In 1997, the US Food and Drug Administration Modernization Act mandated identification and quantification of mercury in all food and drugs. The subsequent FDA review noted that with the increased number of vaccines then recommended for infants, the total amount of mercury in vaccines containing thimerosal might exceed the levels recommended by other federal agencies [1]. The mercury limits imposed by these agencies have a wide margin of safety; and there was no information suggesting that any infant had been harmed. Nevertheless, to be super-cautious, the U.S. Public Health Service (PHS) and the American Academy of Pediatrics (AAP) asked doctors to minimize exposure to thimerosal-containing vaccines and manufacturers to remove thimerosal from vaccines as soon as possible [2].

By mid-2000, thimerosal-free vaccines against hepatitis B and bacterial meningitis were widely available. A combination vaccine for diphtheria, pertussis, and tetanus is also available today without thimerosal. Measles/mumps/rubella (MMR), chickenpox, inactivated polio, and pneumococcal conjugate vaccines have never contained thimerosal. Thus, except for some influenza vaccine, none of the vaccines now used to protect preschool children against 12 infectious diseases contain thimerosal as a preservative. Certain flu vaccines and tetanus-diphtheria vaccines (Td) given to children age 7 and older still contain thimerosal as a preservative.

Before the recent reductions, the maximum cumulative exposure to mercury via routine childhood vaccinations during the first six months of life could have been 187.5 micrograms (which averages to about 1 microgram per day. With the newly formulated vaccines, the maximum cumulative exposure during the first six months of life should now total no more than 3 micrograms of mercury [3]. No studies have shown that either the old or the new amounts have any toxic effect.

The U.S. Centers for Disease Control and Prevention has compared the incidence of autism with the amount of thimerosal received from vaccines. Preliminary results indicated no change in autism rates relative to the amount of thimerosal a child received during the first six months of life (from 0 micrograms to greater than 160 micrograms). A weak association was found with thimerosal intake and certain neurodevelopmental disorders (such as attention deficit hyperactivity disorder) in one study, but was not found in a subsequent study [4]. Additional studies are planned, but it is unlikely that any significant association will be found.

An Institute of Medicine (IOM) committee, which issued a comprehensive report in October 2001, found no proof of a link between thimerosal-containing vaccines and autism, attention deficit-hyperactivity disorder, speech or language delays, or other neurodevelopmental disorders [5].

A study published in 2002 of infants who were 6 months of age or younger compared the levels of mercury in the blood, hair, urine, and stool of 40 who received vaccines containing thimerosal and 20 who received vaccines without thimerosal. The study found:

  • Mercury levels in blood and urine were low in all infants studied and in many cases too small to measure. There was no observed dose-dependent relationship between the level of thimerosal received through vaccination and the level of mercury in the body.
  • Mercury levels in blood did not exceed, at any time, the blood levels that correspond to Environmental Protection Agency guidelines for exposure.
  • Mercury levels in the stool of infants receiving vaccines containing thimerosal were relatively high compared to mercury levels in the stool of infants who were not exposed to thimerosal, providing evidence that mercury from thimerosal is eliminated in the stool of infants.

The researchers concluded that, “Administration of vaccines containing thimerosal does not seem to raise blood concentrations of mercury above safe values in infants.” [6].

Seven studies reported between 2003 and 2006 found no association between exposure to thimerosal in vaccines and the incidence of autism [7].

Thimerosal was eliminated from most vaccines in 2001. If it actually caused autism, the removal would be followed by a sharp drop in the number of newly diagnosed cases. However, in 2007, a study of autism rates in California found that no drop occurred [8]. The data were published in the Archives of General Psychiatry accompanied by an editorial that stated:

Parents of autistic children should be reassured that autism in their child did not occur through immunizations. Their autistic children, and their siblings, should be normally vaccinated, and as there is no evidence of mercury poisoning in autism, they should avoid ineffective and dangerous “treatments” such as chelation therapy for their children [9].

The Bottom Line

The use of chelation therapy to treat autistic children is completely bogus. Several lawsuits have been filed by parents who were victimized in this way [10].

  1. Ball L and others. An assessment of thimerosal in childhood vaccines. Pediatrics 107:1147-1154, 2001.
  2. Thimerosal in vaccines: A joint statement of the American Academy of Pediatrics and the Public Health Service. Mortality and Morbidity Weekly Report 48:563-565, 1999.
  3. Thimerosal & vaccines: Q&A. CDC Immunization Program Web site, revised May 18, 2004.
  4. Thimerosal in vaccines. FDA Center for Drug Evaluation and Research, Nov 13, 2001.
  5. Immunization Safety Review Committee. Thimerosal-Containing Vaccines and Neurodevelopmental Disorders. National Academy Press, 2001.
  6. Pichichero ME and others. Mercury concentrations and metabolism in infants receiving vaccines containing thimerosal: a descriptive study. Lancet 360:1737-1741, 2002.
  7. Gerber JS, Offit PA. Vaccines and autism: A tale of shifting hypotheses. Clinical Infectious Diseases 48:456-461, 2009.
  8. Schechter R, Grether JK. Continuing increases is autism reported to California’s Developmental Services System: Mercury in retrograde. Archives of General Psychiatry 65:19-24, 2008.
  9. Fombonne E. Thimerosal disappears but autism remains. Archives of General Psychiatry 65:15-16, 2008.
  10. Barrett S. Edelson Center closed after three suits alleging fraud and malpractice. Quackwatch, Sept 5, 2006.

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This article was revised on May 27, 2011.