"Mercury has long been known to be a mitochondrial toxin, and could potentially interact with underlying genetic vulnerability of deficient mitochondria," she said. "That said, there remains no epidemiological data that we are aware of that implicates vaccination in autism or in mitochondrial disorders."
And vaccine experts said the victory for the Polings may represent a defeat for an important public health measure. Dr. William Schaffner, professor and chairman of preventive medicine at Vanderbilt University, said he believes the concession should not have been made until more evidence suggesting exactly how the vaccines may have contributed to Hannah's condition come to light.
"It appears that the judges in this case have not only made a legal decision but also a medical and scientific decision," he said. "I don't believe the court's role is to make these decisions."
"Legal action does not equate with proof," agreed Dr. Ira Rubin of Naperville Pediatrics in Naperville, Ill. "How many times have defendants in cases been found guilty and later found innocent when DNA testing is done?"
This case, as well as other cases involving possible injury brought about by a vaccine, are handled under the National Childhood Vaccine Injury Act of 1986. The act created a no-fault system in which people with grievances, such as the Polings, would file injury claims against the federal government rather than sue the companies that made the vaccine or the health care providers who administered it.
A "special master" appointed by the U.S. Court of Federal Claims reviews these cases to determine whether vaccines were more likely the cause of the injury at hand. If the government chooses not to rebut the claim by showing that the vaccine probably was not responsible for the injury, the claim is approved and an award is made.
The legal standard set by this system is therefore a much lower bar than the demands of medical validity, which would require a much greater magnitude of evidence to draw the conclusion that vaccines were in any way responsible for an injury.
Regardless, the case has brought attention to the nearly 5,000 other families that lawyers have chosen in an effort to seek this compensation from the government, claiming that the mercury-containing preservative thimerosal in vaccines brought about autism and other developmental disorders in their children. Since 2001, the ingredient has been absent from most vaccines, save for certain influenza shots.
Past studies in Denmark, and more recently California, have suggested that thimerosal was not to blame, as reported cases of autism have continued to increase after the removal of thimerosal from most vaccines. Boyd Haley, a chemist at the University of Kentucky and vocal proponent of a vaccine-autism link, believes these studies are flawed. And he said that he believes this case, as well as most other cases of autism, are indeed the result of an underlying genetic vulnerability being triggered by the mercury that used to be present in vaccines.
"I am very pro-vaccine," Haley said. "I strongly believe in vaccination. I just believe that they ought to be safe and they ought to be tested."
Specifically, Haley said certain genetic conditions may make some children unable to effectively manufacture glutathione, a protein he says would allow them to clear substances such as mercury from their systems. Autism, he said, could be the result.