Confessions of a Quackbuster

This blog deals with healthcare consumer protection, and is therefore about quackery, healthfraud, chiropractic, and other forms of so-Called "Alternative" Medicine (sCAM).

Monday, December 05, 2005

Thimerosal information needs clarification

An excellent Letter to the Editor:

Monday December 5, 2005

Thimerosal information needs clarification

Seriously flawed information regarding thimerosal in vaccines appeared in Anne McElroy Dachel's letter to the editor (11/24/05).

In such a target-rich environment, it is hard to know where to start first. Let's start with her contention that the lack of evidence of harm comes from "the CDC's easily flawed and manipulated population studies."

To the contrary, numerous large epidemiologic studies from the United States, Britain and Denmark have failed to find a link between thimerosal exposure and autism, Asperger's syndrome or other autistic-spectrum disorders. In a presentation by Dr. Elizabeth Miller to the Institute of Medicine's Immunization Safety Review Committee last year, she reviewed an analysis of 103,043 children born in Great Britain between 1988 and 1997. The children received a cumulative mercury dose of 75 micrograms (mcg) in their diptheria, tetanus and pertussis (DTP) vaccine doses by 4 months of age and were followed for at least eight years.

Paradoxically, the DTP vaccine seemed to be protective against the development of autism.

In perhaps the largest cohort studied, Anders P. Hviid of the State Serum Institute in Copenhagen studied the cohort of all children born in Denmark between Jan. 1, 1990, and Dec. 31, 1996 (467,450 children), comparing children vaccinated with thimerosal-containing vaccines with children vaccinated with thimerosal-free versions of the same vaccines. After 1992, the government quit producing the thimerosal version. Results of the study published in JAMA Oct. 1, 2003, found "the risk of autism and other autistic-spectrum disorders did not differ significantly between children vaccinated with thimerosal-containing vaccine and children vaccinated with thimerosal-free vaccine." Moreover, no dose-response association was noted. Interestingly, Hviid noted no decrease in the rate of autism in Denmark after thimerosal was removed from the DTP vaccine.

The cause of autistic-spectrum disorders remains unknown, but the increase has been documented in foreign countries that either discontinued use of thimerosal in vaccines or never used it in the first place. It is at least as likely that the increase is due to changes in diagnostic criteria or increased awareness of the disorders by parents and physicians as childhood vaccines.
These disorders are usually diagnosed in the first two years of life when multiple vaccines are given, suggesting the logical fallacy post hoc ergo propter hoc (after this, therefore because of this). More simply, association (an action followed by a result) does not equal causation (an action causing a result).

While the subject of preservatives in vaccines may seem arcane, the sort of misinformation and junk science presented in Ms. Dachel's letter is all too common on the Internet (and the advertisements of personal injury attorneys), needlessly frightening parents and leading them to trade the small risk of vaccine injury for the all too real risk of the actual disease. For those wishing to know the actual risks involved without the hysteria of some of the anti-vaccination Web sites, I recommend checking out for a more reasoned discussion of the issues involved.

David E. Hanson, M.D.


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