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Brain & Nervous System Health Center

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Thimerosal: No Smoking Gun

CDC: No Evidence of Child Brain Damage Due to Vaccine Preservative

Thimerosal and Tics continued...

One of those worse outcomes was a slightly increased risk of tics -- repetitive physical motions or vocalizations. What makes the finding plausible is that two previous studies identified tics as a possible thimerosal side effect.

However, there is good reason to think that the tic finding was simply chance:

  • The significant finding for tics came from observers who saw the child only once. Parents of children with the highest thimerosal exposure reported no more child tics than parents of children with lower thimerosal exposure.
  • The finding applied to boys, but not to girls.
  • The tic finding included transient tics, which experts do not consider a problem.

WebMD asked pediatric neurologist Jonathan W. Mink, MD, PhD, to comment on the CDC study. Mink is chief of child neurology at the University of Rochester, N.Y., and co-chairman of the scientific advisory board for the Tourette Syndrome Association. He was not involved in the CDC study.

"Tics are seen quite commonly in kids with autism. But most kids with tics don't have autism," Mink tells WebMD. "The bottom line is that the rate of tics here is well within the rate we would expect to see in 7- to 10-year-old kids. Some of them have transient tics, which would go away, and some have tics that will never be a problem."

The bottom line, Mink says, is that the study gives "no reason to think that thimerosal or vaccination causes tics."

No Proof of Thimerosal Safety

The CDC asked more than a dozen outside consultants to comment on the study prior to publication of the final manuscript. One was Sallie Bernard, the parent of a child with autism and executive director of Safe Minds. Safe Minds is one of the groups working to convince parents that medical use of mercury causes autism and other child health problems.

Bernard formally dissents with the CDC's conclusion that the study "does not support a causal association between early exposure to mercury from thimerosal-containing vaccines and immune globulins and deficits in neuropsychological functioning at the age of 7 to 10 years."

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