Ask the Doc: Nov. 2004

I keep hearing about Thimerosal and how it may be dangerous to children. I asked my pediatrician about it, but he basically said there's nothing to worry about. However, I also read that the CDC and FDA asked drug manufacturers to voluntarily remove it from vaccines as soon as possible. How worried should I be about this-and what, if anything, can I as a parent do to protect my child?

Great timely question! I have received this question on several occasions through my own patients, especially with the concern over the flu vaccine shortage. As a whole, the health care community has been uncertain about whether thimerosal, a mercury-based preservative found in some vaccines, is a contributing factor for the seeming increased prevalence of autistic disorder. When normal doses of vaccines containing thimerosal have been given, hypersensitivity has been noted, but no other harmful effects have been reported. However, massive overdoses from inappropriate use of thimerosal-containing products have resulted in toxicity. The U.S. Food and Drug Administration (FDA) has determined that infants who receive thimerosal-containing vaccines at several visits may be exposed to more mercury than recommended by federal guidelines for total mercury exposure. In response to the concern over mercury toxicity in children, the American Academy of Family Physicians (AAP) committees made the following recommendations in September 1999:

1. All children should be immunized against the diseases listed in the Recommended Childhood Immunization Schedule of the AAP, the American Academy of Family Physicians and the Advisory Committee on Immunization Practices.

2. The use of vaccines containing thimerosal should be reduced or eliminated. Benefits and risks of such vaccines should be discussed with parents. However, the use of vaccines containing thimerosal is preferable to withholding vaccination.

3. The FDA and vaccine manufacturers are asked to reduce or eliminate mercury-containing preservatives in vaccines.

4. Infants and children who have received thimerosal-containing vaccines do not require testing for mercury because the concentrations would be low and would not require treatment.

5. Your physician should counsel parents about reducing exposures to other sources of mercury.

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. 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. Additional studies are planned.

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.

Today most manufactures have already eliminated thimerosal in their vaccines so you really do not need to do anything. Check with your doctor to make sure your child is receiving thimerosal-free vaccines whenever possible.