A little over a year ago, if someone had asked me what thimerosal was I would not have had a clue. But since then, I have been exposed to countless Web sites and online forums decrying the evils of this mercury-based preservative once commonly used in childhood vaccines.

A few years ago, as a result of the frightening increases in the incidence of autism as well as suggestions that the increases were due to thimerosal, parents started getting squirmy about vaccinating their kids. In an effort to alleviate parental fears, pediatricians and the public health community rightly asked pharmaceutical companies to remove the preservative from vaccines.

This was done despite a lack of scientific evidence of a causal link between it and autism (or any other problem for that matter). In fact, just last month, the Institute of Medicine released a monumental report that indicated that existing research showed that any link between thimerosal and autism was only theoretical.

Ultimately, for the sake of protecting universal immunization rates, the medical and public health practioners realized it was better to remove the obstacle than to engage in a philosophical debate on the topic on a patient-by-patient basis. The pharmaceutical companies honored the request and since 2000, commonly used vaccinations in the U.S. have been free of the preservative.*

I think we can all agree that we are better off with the removal of the mercury, no matter how trace the amount was. Goodness knows that given all the warnings about mercury in fish,** I am as paranoid as can be. Ahi (tuna) is right up there on my list of favorite foods, but as a breastfeeding mom I feel guilty eating it with the risk of passing the mercury on to my son. So it is nice to be spared the concern when it comes to whether or not to immunize him.

Unfortunately, despite the fact that thimerosal was virtually eliminated nearly four years ago, if you read anti-vaccination Web sites and comments in online forums, you could easily conclude children are still routinely exposed to it. This is where I get frustrated. While I can applaud activists who helped convince doctors and the pharmaceutical companies that it was a good idea to remove the thimerosal, I am sickened by the fact that they continue to frighten parents by implying that it is still used.

Today the Los Angeles Times reported that results of a new study demonstrated that when exposed to thimerosal, a specific strain of mice already predisposed to autoimmune diseases*** exhibited autism-like behaviors. Three additional strains of mice without that genetic predisposition did not exhibit any changes after the thimerosal exposure. This study is fascinating because it reinforces the theory that there is likely a genetic predisposition to autism and that environmental factors could influence the onset of autism among those predisposed.

The study may help deepen our understanding of autism and related disorders and I hope it will lead to additional research. Unfortunately, rather than being seen as a data point for understanding a complex issue, anti-vaccination advocates will tout the study as conclusive and use it to push a social and political agenda challenging universal immunization efforts. Case in point, mercola.com’s headline for the story reads: Thimerosal in Childhood Vaccines Increases Risk of Autism-Like Damage.

This headline is an is a classic example of how those opposed to U.S. immunization policies routinely mislead parents to believe that vaccines are more harmful than the diseases they were designed to prevent. These deceptive practices are the latest addition to the long line of my pet peeves.

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*Commonly used injectable-flu vaccines have thimerosal. Also, while thimerosal is no longer an active ingredient in the vaccines, trace amounts may be present as a result of the production process. Check out the FDA chart detailing amounts present.

**It is important to stress that the mercury in fish (methylmercury) and the mercury in thimerosal (ethylmercury) are NOT the same thing. Check out the CDC’s Web site for more information. While there is significant documentation of the harms of the methylmercury found in fish, there is not a body of evidence indicating harms directly related to ethylmercury.

***Autism is not an autoimmune disease, but some research suggests that those with family history of autoimmune disorders may be predisposed to autism.