Study says vaccine preservative safe

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 the early 1990s, thousands of healthy Italian babies in a study of whooping-cough vaccines got two different amounts of the preservative thimerosal (pronounced thih-MEHR'-uh-sawl) from all 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, to be released today.

Only 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 scientific 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.

Thimerosal, used in some vaccines to prevent the growth of bacteria and fungus, hasn't been in U.S. childhood vaccines since 2001, except for certain flu shots. Italy and other European nations began removing it in 1999. U.S. health officials recommended the removal of thimerosal as a precaution and to reduce the overall exposure of children to mercury.

Safety regulations still require multidose vials of vaccines to contain some type of preservative to prevent the spread of infection from contaminated vials.

The study was funded by the U.S. Centers for Disease Control and Prevention.

The children received either 62.5 micrograms or 137.5 micrograms of ethyl mercury from all their shots during their first year of life. Thimerosal breaks down as ethyl mercury in the body. Before the reduction of thimerosal in the United States, the maximum exposure for infants was 187.5 micrograms of ethyl mercury.

The researchers found the children in both groups scored, on average, in the normal range on 11 tests of memory, attention, motor skills and other brain functions.

Those 11 tests included 24 measured outcomes. Small, but statistical differences were found for only two of those areas, and only for girls. There were no differences in boys.