Recently a mother asked me whether vaccines given to children could cause autism.

The mother has heard that Thimerosal, a mercury-containing compound used as a preservative in the vaccines may be the culprit. Since 1930s this chemical has been used in vaccines and ointments to prevent the growth of bacteria and fungi.

Now there are almost 4,900 claims pending in the U.S. Court of Justice from families alleging that vaccines with Thimerosal have caused autism in their children.

Do vaccines with Thimerosal cause autism? What are the concerns raised by scientists regarding Thimerosal and autism?

In the United States, data from 2000-2001, as compared to that from 1992-1993, showed an enormous increase in the incidence of autism— 644 percent — in children.

This is not solely due to increased awareness in diagnosis by the medical community.

The usage of mercury containing vaccine numbers increased during this period as well. It is a fact that mercury is a neurotoxin. The mercury compound is available in methyl and ethyl forms.

Pregnant women who consumed the methyl mercury in large doses had children with neural damage. So the hypothesis was proposed that mercury in vaccines could cause neural diseases such as autism.

There are many studies discrediting any connection between Thimerosal and autism. I will note a few here. Dr. Robert Schechter and coworkers have analyzed autism data in California from 1995 to 2007 (Arch. Gen. Psy, 2008). The estimated prevalence of autism for children at each year of age from 3 to 12 years increased through the study period, even after Thimerosal was discontinued in the vaccines in 2001.

The prevalence increased 0.6 per 1,000 live births to 4.1 per 1,000 live births, from January 1995 to March 2007. The authors concluded that Thimerosal in vaccines did not cause autism, as the numbers increased even after discontinuation of the chemical. A similar study in Denmark (JAMA, 2003) showed rising incidence of autism even after removal of mercury in the vaccines.

Jon Heron studied 14,000 children in the United Kingdom and found no connection between Thimerosal and autism (J. of pediatrics, 2004). A Canadian study by Eric Fombonne (pediatrics, 2006) analyzed 28,000 children born between 1987 and 1998 who were exposed to varied doses of Thimerosal and found no relationship between the doses of the chemical and autism.

At one time, measles, mumps and rubella vaccine was implicated as a cause of autism. In 2004, the Institute of Medicine reviewed 200 studies related to autism and found no link between MMR or Thimerosal and autism.

Finally, the signs and symptoms of mercury poisoning and autism are dissimilar.

Mercury poisoning causes unsteady gait and dysarthria (difficult, poorly pronounced speech such as slurring). In autism, movements are stereotypic (repetitive, often rhythmic, purposeless movements); speech is delayed and echolalic (echolalia is the repetition of sounds made by another person).

Depression, psychosis and peripheral nerve damage, such as diminished or loss of sensations are noticed in mercury poisoning. In autism, aloofness and antisocial behavior and sensory hyper-responsiveness are noticed (e.g., they may close their ears for ordinary sounds). If Thimerosal has caused damage, autism symptoms should mimic that of mercury poisoning, which is not the case.

If you are still worried, in the next flu season request your doctor to give your child Thimerosal-free flu vaccine. Vaccines are safe; occasionally they can cause complications. However, the complications of the diseases the vaccines prevent are much more serious and deadly.

-- Contact Dr. Raghavendra Rao at usharagu1@yahoo.com.