CHICAGO — A new study from Italy adds to a mountain of evidence that a mercury-based preservative once used in many vaccines doesn’t hurt children, offering more reassurance to parents.
In Italy in the 1990s, thousands of healthy babies in a study of whooping-cough vaccines got different amounts of the preservative thi mer osal from their routine shots.
Ten years later, 1,403 of those children took a battery of brain- function tests. Researchers found small differences in only two of 24 measurements, and those “might be attributable to chance,” they wrote in the February issue of the journal Pediatrics, released today.
One case of autism was found, and that was in the group that got the lower level of thimerosal.
Autism is a complex disorder featuring repetitive behaviors and poor social interaction and communication skills. Scientists generally believe genetics plays a role in causing the disorder; a theory that thimerosal is to blame has been repeatedly discounted in studies.
“Put together with the evidence of all the other studies, this tells us there is no reason to worry about the effect of thimerosal in vaccines,” said the new study’s lead author, Dr. Alberto Tozzi of Bambino Gesu Hospital in Rome.
The debate over thimerosal and autism has been much stronger in the United States than in Italy, Tozzi said. But the researchers recognized a chance to examine the issue by going back to the children who had taken part in the 1990s whooping-cough research.
Randomization sets the new study apart. The random assignment of children rules out the chance that factors other than thimerosal, such as education or poverty, caused the results.
