About 5,000 families have filed claims involving autism, a spectrum of developmental disorders whose hallmarks are impaired social interaction and communication.
The appointed judicial officers in this case, known as special masters, decided to hear test cases on different causation theories to develop general principles that they could apply to the flood of claims.
Three special masters heard the cases of the Cedillo, Hazlehurst and Snyder families in 2007. Lawyers for the families argued that vaccines containing thimerosal weakened the children's immune systems, allowing the viruses in the MMR vaccine to take hold and lead to autism.
In the Hazlehurst case, lawyers for the family came to argue that the MMR vaccine was the primary culprit.
Thimerosal was used to keep bacteria from growing in multidose containers. The MMR vaccine never contained thimerosal, but some other routinely recommended vaccines such as the hepatitis B vaccine did.
Thimerosal was phased out of most shots around 2000. Trace or small amounts of thimerosal remain in a few vaccines recommended for children, including the flu shot.
Arguments rejected
The special masters rejected practically all of the families' arguments.
"I concluded the evidence was overwhelmingly contrary to the petitioners' contentions," George L. Hastings Jr. wrote in the Cedillo opinion, which was similar to the others.
"The expert witnesses presented by the respondent were far better qualified, far more experienced and far more persuasive than the petitioners' experts."
Several parent-advocates were frustrated by the decisions.
"I'm sure the decision was based on some of the current science that is out there and the scientific community hasn't invested in the types of independent research necessary to get to the bottom of the issue," said Rick Rollens, the parent of an autistic son and co-founder of the University of California, Davis M.I.N.D. Institute.
Rollens and others said these verdicts won't make parents stop questioning the safety of vaccines, especially when parents witness changes in their children right after vaccination.
"There's no denying what happens to your child when you see it first-hand," said Rollens, a Sacramento, Calif., resident. "Maybe we haven't asked all the right questions yet."
The special masters are still working on another group of test cases alleging that the thimerosal itself causes autism.
Final briefs on those cases are still being filed, with decisions expected after the summer.
Yesterday's decisions "won't resolve the thimerosal cases," said Webb. "There are more people that focus on thimerosal than focus on MMR. ... Those cases are still viable."
