Thiomersal controversy

The thiomersal controversy describes claims that vaccines containing the mercury-based preservative thiomersal contribute to the development of autism and other brain development disorders. Thimerosal is no longer used in children's vaccines in the United States, except some types of flu shots. While exposure to mercury may result in damage to brain, kidneys, and developing fetus, the current scientific consensus has found no convincing scientific evidence supporting claims that thiomersal has such effects.

Thiomersal (also spelled thimerosal, especially in the United States) is an organomercury compound used as a preservative in vaccines since the 1930s to prevent bacterial and fungal contamination. Following a mandated review of mercury-containing food and drugs in 1999, the Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP) asked vaccine makers to remove thiomersal from vaccines as quickly as possible as a precautionary measure, and it was rapidly phased out of most U.S. and European vaccines. It is still used in all multi-dose vials of flu vaccines in the U.S. In the context of perceived increased autism rates and increased number of vaccines in the childhood vaccination schedule, some parents believed the action to remove thiomersal was an indication that the preservative caused autism.

The potential impact of thiomersal on autism has been investigated extensively. Multiple lines of scientific evidence have shown that thiomersal does not cause autism. For example, the clinical symptoms of mercury poisoning differ significantly from those of autism. In addition, multiple population studies have found no association between thiomersal and autism, and rates of autism have continued to increase despite removal of thiomersal from vaccines. Thus, major scientific and medical bodies such as the Institute of Medicine and World Health Organization (WHO) as well as governmental agencies such as the Food and Drug Administration (FDA) and the CDC reject any role for thiomersal in autism or other neurodevelopmental disorders. In spite of the consensus of the scientific community, some parents and advocacy groups continue to contend that thiomersal is linked to autism.

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