The CDC researchers didn't find a clear link between early exposure to thimerosal and problems with brain function and behavior in children ages 7 to 10. The results are in line with past research that found no connection between vaccines and neurological problems or autism, the Associated Press writes.
"It's good news for families," says Michael Goldstein, vp of the American Academy of Neurology who works in private practice in Salt Lake City. "There's no evidence that these vaccines have caused injury."
As with any study, though, there are reasons for pause. For instance, among girls there was a negative association with language development. And among boys there was a detrimental association with behavioral regulation and motor and phonic tics, suggesting the need for further study. So after you've read the study (here it is, again), please tell us your reaction. (If you have difficulty voting, simply access a browser other than AOL. Sorry for any inconvenience).
Do you feel reassured by the study?
- No (90%, 287 Votes)
- Yes (10%, 33 Votes)
Total Voters: 320
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Thimerosal, by the way, hasn't been used in childhood vaccines since 2001, although it's still in some flu shots. The new findings apply to kids immunized before then, or exposed to the preservative through shots their mothers received while pregnant. (Thimerosal was put in vaccines to prevent contamination from bacteria).
The study involved 1,047 children who were exposed to varying levels of thimerosal while in the womb or after birth in the 1990s. The children belonged to four health maintenance organizations that are part of a federal project to study the side effects of vaccines. Their mercury exposure was determined through medical and immunization records and interviews with parents.
Each child was tested for speech and language skills, motor coordination and intelligence. Parents, teachers and trained specialists also rated stuttering, attention span and tic disorders such as head shaking, eye blinking and neck jerking. A total of 42 neurological problems were analyzed.
On balance, researchers did not find a consistent pattern between increasing thimerosal exposure and the risk of these problems. However, they said one finding merited further study: Boys exposed to higher mercury levels seemed to have more tic problems -- a link seen in previous research.
"The doses of mercury that children were exposed to because of immunization doesn't cause neuropsychological damage," says Bruce Cohen, a Cleveland Clinic pediatric neurology specialist who had no role in the study.
The CDC study was reviewed by an independent panel of scientists and statisticians who oversaw its design, reviewed results and contributed to writing the report. The panel included one vaccine opponent - Sallie Bernard, executive director of the consumer group SafeMinds. Although she had a role in planning the study, she asked to be listed as a "dissenting member" because she disagreed with the study's conclusions.
The research was led by William Thompson, a CDC epidemiologist who once worked for vaccine maker Merck. Four other researchers have received fees from drugmakers and one has served as a consultant to a CDC committee on immunization.
The study wasn't designed to tease out the effects of mercury exposure on autism. Thompson is completing a separate study examining whether thimerosal exposure before or after birth causes autism. The study recruited 1,000 children including 250 with autism. Results are expected next year.
Although past scientific studies have found no link between autism and thimerosal-containing vaccines, the highly charged issue went on trial this summer. A court in Washington, D.C., heard from an Arizona mother who blamed vaccines on her 12-year-old daughter's severe autism. The case is being followed by about 5,000 families who filed similar claims to receive compensation from a federal vaccine injury fund. The fund so far has not paid out an autism claim.