Skip to content

Brain & Nervous System Health Center

Thimerosal: No Smoking Gun

CDC: No Evidence of Child Brain Damage Due to Vaccine Preservative
Font Size
A
A
A
By
WebMD Health News
Reviewed by Louise Chang, MD

Sept. 26, 2007 - Thimerosal in vaccines has not affected children's brains or behaviors, the CDC says.

Thimerosal is a mercury-based preservative once common in vaccines. It's now found only in small amounts in some flu vaccines. However, thimerosal was once used in most vaccines given to children.

Although the amounts were tiny, they added up. Because symptoms of autism often appear suddenly around age 1 -- when kids have received a number of vaccinations -- many parents became convinced that thimerosal caused their children's autism. But the Institute of Medicine has twice rejected this idea.

The new CDC study carefully avoided the still-controversial issue of whether thimerosal is linked to autism. A separate CDC study of this issue is under way, with a report expected in a year's time.

"In this study there is nothing you can draw on regarding any relationship to autism," researcher William W. Thompson, PhD, of the CDC's National Immunization Program, said at a news conference.

Instead, the study looked for 42 different neurological and psychological problems in more than 1,000 7- to 10-year-old children exposed to various amounts of thimerosal while still in the womb, from birth to 28 days, or up to age 7 months.

"This was a large, very careful study to determine whether thimerosal exposures in early childhood was associated with bad neuropsychological outcomes," Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases, said at the news conference. "It came out with very reassuring results."

"Ninety-eight percent of the answers here are very reassuring," John Iskander, MD, MPH, acting director of the CDC's Immunization Safety Office, said at the news conference.

Thimerosal and Tics

What about the other 2% of the study findings? The study looked at 42 different outcomes, ranging from intelligence to fine motor coordination. The researchers performed 378 statistical tests on the data. Each statistical test had 5% odds of being a chance finding.

"By chance alone we would estimate about 5% of test results would be significant," Schuchat said. "And in fact that is exactly what we found: 19, or 5%, of the statistical tests did find significant results. They were pretty evenly split between [linking] better and worse outcomes [to thimerosal]."

1 | 2 | 3

Today on WebMD

nerve damage
Learn how this disease affects the nervous system.
senior woman with lost expression
Know the early warning signs.
 
woman in art gallery
Tips to stay smart, sharp, and focused.
medical marijuana plant
What is it used for?
 
senior man
Article
boy hits soccer ball with head
Slideshow
 
Graphic of active brain
Article
Vaccine and needle
VIDEO
 
brain illustration stroke
Slideshow
human brain
Article
 
most common stroke symptoms
Article
Graphic of number filled head and dna double helix
Quiz