Study says childhood vaccine component thimerosal not linked to neuropsychological problems

Sep 27 2007

According to the latest research on the affect of thimerosal (mercury) in vaccines on the neuropsychological functions of children's brains, the evidence suggests there is no association.

The researchers at the Centers for Disease Control and Prevention (CDC) say mercury-based vaccines did not appear to affect children's verbal ability, fine motor control, memory and attention.

The study is the first of a series which aim once and for all to settle the controversy over thimerosal.

The CDC study involved more than 1,000 children aged 7 to 10 and showed that having been exposed to thimerosal in vaccines before and after birth did not affect neuropsychological functions; the study did not look at autism which is focus of another study due for release next year.

Dr. William Thompson of the U.S. Centers for Disease Control and Prevention, who led the study says the weight of the evidence suggests there is no association

Dr. Thompson says of the 42 neuropsychological outcomes, only a few significant associations with exposure to mercury from thimerosal were detected, which were small and almost equally divided between positive and negative effects.

Thompson says that probably means that any associations were by chance, but the only exception was a type of tic called a motor tic, which seemed to be more common among boys who received thimerosal.

According to the CDC researchers the tic was so subtle and most commonly marked by finger-tapping that none of the children's parents had noticed.

Dr. Anne Schuchat, director of the CDC's National Immunization Program, says the study produced no massive surprising results and the findings are very reassuring.

Thimerosal has been used as a preservative in vaccines for decades and though it contains mercury, the mercury is in a chemical form called ethyl mercury that scientists say cannot affect the body in the same way that methyl mercury can which is found in contaminated fish.

Alarm was first raised when activists began to link cases of autism to vaccines and eventually, thimerosal was targeted as the most likely culprit.

Even though the CDC has always maintained that thimerosal is safe, they eventually persuaded manufacturers to remove it from all childhood vaccines except for flu shots by 2001.

But this has done little to reassure some parents and more than 5,000 families have filed claims with the federal Vaccine Injury Compensation Program.

Criticism that the CDC was guilty of bias led many to question studies that purported to show thimerosal and vaccines were safe.

So the CDC has conducted more studies and this one is the first to be completed.

Whether it will resolve the controversy remains to be seen as already one of those involved in the study Sallie Bernard, executive director of one activist group called SafeMinds, disputes the CDC's conclusions.

The study is published in the New England Journal of Medicine.