Government researchers say they found little evidence of a link between vaccinations and developmental problems in a study of more than 140,000 U.S. children.
THE REPORT didn’t satisfy vaccine critics, who claimed the study’s initial results showed a stronger connection but were watered down. They also noted that the study’s lead author now works for a vaccine maker.
The study, published Monday in the December issue of Pediatrics, is one of the latest attempts to determine whether older vaccines with the mercury-containing preservative thimerosal led to nervous-system problems such as autism, as some vocal critics contend.
In one group of children studied, routine vaccines in infancy appeared to slightly increase the risk for tics. In another group, a slight association was seen with language delays but not tics. A third group showed no associations with any disorder.
In all, more than 140,000 children were studied and no link was found with any other disorders, including autism, said co-researcher Dr. Frank DeStefano of the Centers for Disease Control and Prevention.
Many previous studies of vaccines containing the preservative thimerosal also failed to find strong evidence of any link.
The new results are reassuring, DeStefano said, and more definitive answers are expected from in-person examinations the CDC is giving some of the study participants.
But Dr. Mark Geier, a geneticist who has worked as a consultant on parents’ lawsuits against vaccine makers, said the researchers’ own earlier analysis of the study results found strong links between vaccines and such problems — and that the published results attempt to conceal those findings. He claimed the final analysis “is intentional fraud.”
DeStefano acknowledged that the early results suggested stronger links with some disorders, though not autism, but denied that there had been pressure or a cover-up. He said the final data reflect a more thorough recent analysis.
The study’s lead author, former CDC researcher Dr. Thomas Verstraeten, now works for vaccine maker GlaxoSmithKline in Belgium, and Geier said that connection may have influenced how the research was reported.
Verstraeten, who left the CDC in July 2001, did not respond to an e-mail request seeking a response, and company spokeswoman Nancy Pekarek said he did not wish to discuss the results. She provided a written statement in which Verstraeten indicated that since leaving the CDC he has worked only as an adviser as the study was finalized and prepared for publication.
The researchers analyzed data from three health maintenance organizations on children born between 1992 and 1999 and tracked for several years. Information was gathered on several neurodevelopmental disorders, including autism, attention deficit disorders, stammering and emotional disturbances.
While the researchers were beginning to examine their results, public health officials were beginning to publicly address concerns about the use of thimerosal in childhood vaccines.
Mercury in high doses has been linked with neurodevelopmental problems. Parents and others worried about potentially dangerous overexposure to thimerosal because of the increasing number of vaccines recommended in childhood.
Vaccine makers have since phased out use of thimerosal as a preservative in childhood vaccines used in the United States, though trace amounts remain in some vaccines.
It is still used as a preservative elsewhere, especially in developing countries, said Dr. Thomas Saari, a member of the American Academy of Pediatrics’ infections diseases committee and a pediatrics professor at the University of Wisconsin in Madison.
Vaccine expert Dr. Neal Halsey of Johns Hopkins University said the study shows that if there is any association between older vaccines and mild disorders, “it must be relatively small.”
“A major health risk should have shown up in a consistent pattern in all three of the HMOs,” Halsey said.
Still, he said the findings might have been different if the researchers had done a separate analysis by gender, since boys are much more susceptible to mercury exposure than girls.