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No correlation between thimerosal-containing vaccines and autism

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Commentary on thimerosal and autism in Denmark

Despite the consensus view that autism is a neurodevelopmental disorder originating during early fetal life and is probably due to a faulty genetic program for brain development, there is a widespread belief that affected children were "normal" at birth and later sustained an injury causing autism. The cluster of autism cases in Brick Township, New Jersey suggests an environmental factor. Although there are myriad other possibilities for an environmental toxin, many parents believe that vaccines caused autism in their children. Because of the coincidence of MMR vaccination (which is generally administered between 15 and 18 months of age) and autistic regression (which occurs in about one-quarter of children with autism), this vaccine has been implicated despite several epidemiologic studies that have failed to show a correlation between MMR and the incidence of autism. Moreover, many parents believe that MMR vaccine contains mercury. In point of fact, it never contained thimerosal, an organic mercurial compound used in other vaccines to prevent bacterial contamination. However, until recently a number of other vaccines contained mercury. At the behest of public health experts and the American Academy of Pediatrics, infants no longer receive thimerosal-containing vaccines with the exception of influenza ("flu shot"). It is expected that thimerosal will be phased out of the influenza vaccine in the near future.

An article in the September 2003 issue of PEDIATRICS (published by the American Academy of Pediatrics) is abstracted below. Denmark has a universal system of health care and maintains complete registries of health status, including mental health disorders and immunization status. Researchers were able to track the incidence of autism in Denmark during the period, 1971-2000. Thimerosal was used in vaccines from 1971 through 1990. During this period, there was no increase in the incidence of autism. However, an increase in autism occurred between 1991 and 2000, during a period when thimerosal-containing vaccines were not used. These data are good evidence that thimerosal does not play a role in the incidence of autism.

Ronald Kallen, MD
September 25, 2003


Abstract of article in September 2003 issue of PEDIATRICS

Title: Thimerosal and the occurrence of autism: Negative ecological evidence from Danish population-based data.

Authors: Madsen KM, Lauritsen MB, Pedersen CB, Thorsen P, Plesner A-M, Andersen PH,, Mortensen PB

Publication: PEDIATRICS 2003 (September); 112(3):604-606.

Objective: It has been suggested that thimerosal, a mercury-containing preservative in vaccines, is a risk factor for the development of autism. We examined whether discontinuing the use of thimerosal-containing vaccines in Denmark led to a decrease in the incidence of autism.

Design: Analysis of data from the Danish Psychiatric Central Research Register recording all psychiatric admissions since 1971, and all outpatient contacts in psychiatric departments in Denmark since 1995.

Patients: All children between 2 and 10 years old who were diagnosed with autism during the period from 1971-2000.

Outcome measures: Annual and age-specific incidence for first day of recorded admission with a diagnosis of autism in children between 2 and 10 years old.

Results: A total of 956 children with a male-to-female ratio of 3.5:1 had been diagnosed with autism during the period from 1971-2000. There was no trend toward an increase in the incidence of autism during that period when thimerosal was used in Denmark, up through 1990. From 1991 until 2000 the incidence increased and continued to rise after the removal of thimerosal from vaccines, including increases among children born after the discontinuation of thimerosal.

Conclusion: The discontinuation of thimerosal-containing vaccines in Denmark in 1992 was followed by an increase in the incidence of autism. Our ecological data do not support a correlation between thimerosal-containing vaccines and the incidence of autism.

Abstract copyright 2003 by the American Academy of Pediatrics.

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This page last updated on 09/25/2003