The CDC is continuing to investigate whether a mercury preservative in childhood immunizations has caused cases of autism -- despite the fact a report it paid for said such research should end.
The agency wants to determine whether exposure to the vaccine preservative, called thimerosal, can be linked to autism spectrum disorders, Glen Nowak, director of media relations at the Centers for Disease Control and Prevention, told Age of Autism on Friday.
The study includes 300 children with ASDs, 200 of whom have full-syndrome autism, as well as a comparison group of children who do not have the disorders.
In 2004 a CDC-funded report by the independent Institute of Medicine concluded there was no evidence of a vaccine-autism link and efforts should go instead to "promising" autism research.
"Further research to find the cause of autism should be directed toward other lines of inquiry," the immunization review panel said. "It's really terrifying, the scientific illiteracy that supports these suspicions," said Dr. Marie McCormick, chairwoman of the IOM panel, in a New York Times article in June.
And the head of the CDC's immunization program said the same year that only "junk scientists and charlatans" take such a link seriously.
Nevertheless, spokesman Nowak said the CDC -- which sets the childhood immunization schedule that states adopt -- has not eliminated thimerosal as a suspect.
"We do agree the preponderance of evidence to date suggests there is no association between thimerosal and autism," said Nowak when asked why the CDC was continuing to pursue the issue. But he said CDC Director Dr. Julie Gerberding is committed to exploring all possibilities until the cause or causes of the disorder are identified.
"Dr. Gerberding has made it clear the CDC has not ruled out anything as possible causes of autism, including thimerosal," Nowak said. "Science is a dynamic process. We have continued to fund studies to look at the role, if any, of thimerosal."
The study was designed in 2003 and data collection -- which includes evaluation of each child and their immunization history -- began last year, Nowak said. A letter dated Nov. 8 and an accompanying brochure were provided by a parent who received them.
"In this study, the CDC wants to find out if children who received vaccines and medicines with Thimerosal as infants are more likely to later have developmental problems such as Asperger's Syndrome or autism," says the letter, sent on behalf of the CDC by a research firm and Kaiser Permanente, one of three HMOs involved.
"Your participation in this study may help doctors learn about the possible risks of vaccines and medicines that contained thimerosal."
The mother who received the letter expressed dismay because most medical experts and federal health authorities have reassured parents thimerosal does not cause autism and is not responsible for the large increase in diagnoses beginning in the 1990s.
In 1999 the CDC and the American Academy of Pediatrics urged manufacturers to phase out thimerosal from childhood immunizations as soon as possible, based on the concern that the total amount of mercury received by a child could exceed some government guidelines.
But, citing five subsequent epidemiological studies, the CDC and other health authorities now say there is no evidence of an association.
The CDC continues to recommend flu shots -- most of which contain thimerosal -- for pregnant women and for children 6 to 23 months of age. The agency has declined to express a preference for the thimerosal-free version, citing concern that it might cause some parents to forego immunizing their children against flu if they cannot obtain it.
In addition, tens of millions of children around the world are being injected with thimerosal-containing vaccines, based heavily on the assurances of U.S. health authorities that it is safe and does not cause autism.
Results of the study should be available in September 2007, Nowak said.