WASHINGTON, Dec. 11 (UPI) -- For three years, the CDC has used a study conducted on its own Vaccine Safety Datalink to reassure parents that mercury in vaccines does not cause autism. Now a panel of government-appointed experts says there are "serious problems" with exactly the approach the CDC took.
"I think what we're saying is that (study) wasn't the last word and that things need to be looked at again and perhaps with different methodology," chairwoman Irva Hertz-Picciotto told Age of Autism, which obtained a copy of the panel's report.
Critics said that renders reassurances about the mercury preservative, called thimerosal, unconvincing.
"How can health authorities, with a straight face, claim they have any evidence proving no connection after this report?" asked J.B. Handley, co-founder of Generation Rescue, an advocacy group that believes autism is essentially mercury poisoning by another name.
"This is analogous to our government not finding WMD in Iraq after reassuring the world they would. It's a loss of credibility, and we are back at square one."
The study -- often called the Verstraeten study for its principal author, Dr. Thomas Verstraeten -- used the Vaccine Safety Datalink maintained by the CDC to extract information from records kept by three health maintenance organizations. On its Web site, the CDC says: "(T)he results from this study suggest there is not a 'cause and effect' relationship between thimerosal and autism or ADD (attention deficit disorders)."
But the database has weaknesses -- including different ways of diagnosing autism at different HMOs -- that make it hard to draw broad conclusions, the experts said.
"The panel identified several serious problems that were judged to reduce the usefulness of an ecologic study design using the VSD to address the potential association between thimerosal and the risk" of autism, according to the report. An ecologic study -- analyzing groups rather than individuals -- was the approach the CDC used.
"We actually just got the report and haven't had a chance to assess it," CDC spokesman Glen Nowak said Monday. "Our Office of Science will be working with our Immunization Safety Office in terms of where and how this fits into our research agenda. We've got a couple of other studies under way."
Nowak said that the agency is working to eliminate all remaining thimerosal-containing shots as soon as possible, "so it wouldn't change where we want to go there, either."
He added that limitations of the study were acknowledged by Verstraeten -- who subsequently said its findings were "neutral" and required follow-up. Nowak said several studies support the safety of thimerosal, and he noted the expert panel suggested other ways to look for a possible connection using the database, including comparisons of siblings of those diagnosed with autism.
The panel was convened last May at Congress's request by the National Institute of Environmental Health Sciences, part of the National Institutes of Health. Congress wanted an independent opinion about whether the CDC's Vaccine Safety Datalink could be used to compare autism rates and vaccine mercury before and after thimerosal was phased out beginning in 1999.
That wouldn't work, the panel said, partly because of changes over time, but also because of problems with the data.
"I think there's more work to be done," said Hertz-Picciotto, a professor in the Department of Public Health at the University of California-Davis School of Medicine. She added it's unlikely that autism rates will decline significantly anytime soon.
"It's an 'open question' whether anything about vaccines -- timing, dose, preservative -- is related to the rise in diagnoses," she said.
The study was one of five key epidemiological studies cited by the prestigious Institute of Medicine when it concluded in 2004 that the evidence is against a link between thimerosal and autism.
But Hertz-Picciotto said several of those studies had more problems than the one conducted with CDC data.
"Some studies are stronger than others. The Verstraeten study was an improvement on other studies including the two in Denmark, both of which had serious weaknesses in their designs that limit what we can learn from them," she said.
David Kirby, author of the book "Evidence of Harm" on the controversy over thimerosal and autism, said the Institute of Medicine report -- intended to bring the mercury-autism debate to a close -- is on shaky ground as well.
"This is a strong blow at the very foundation of the 2004 IOM report, which builds its conclusion against causation largely on this (CDC vaccine safety) database.
"I would also point out that all the weaknesses cited by the NIH (expert panel) were highlighted long ago by members of SafeMinds," a group that opposes mercury in medicine.
Kirby said that in 1999, while the CDC's research was under way, SafeMinds' Lyn Redwood met with Verstraeten and raised the same issues: "under-ascertainment of cases, misreporting of data, ignoring prenatal exposure and a 25 percent exclusion rate" of children listed in the databases.
Kirby predicted the Institute of Medicine will now face increased pressure to take a fresh look at thimerosal and autism.
The expert panel's Hertz-Picciotto said research into autism has barely begun.
"We know there's a major genetic component to autism, but genes cannot explain a rise over a short time period of a few decades," she said.
"We also know that environment plays a significant part, and the scientific community is just beginning to search for what those factors and exposures are."