The US government won’t dole out cash to parents who claim that a preservative in vaccines triggered autism in their children.

Several large-scale studies have failed to find a link between vaccines and autism. But that didn’t stop parents from 5000 families who believe there is a link from seeking compensation under the National Vaccine Injury Compensation Program, created to help the small number of children who have severe allergic reactions to vaccines.

On 12 March, the judges overseeing the scheme declared there was no proof that the children’s autism was caused by thimerosal (thiomersal outside the US), a mercury-containing preservative used in some vaccines. The same court had already thrown out claims that thimerosal plus the measles-mumps-rubella vaccine causes autism. “The ruling supported the science,” says Paul Offit of the Children’s Hospital of Philadelphia in Pennsylvania. The families can appeal the decision, but it is unlikely to be reversed.

This may not be the end of the anti-vaccine campaign, however. Campaigners have already started blaming the sheer number of vaccines a child receives, rather than a particular one or combination, for autism. “They keep moving the goalposts,” says Offit. “It’s the hallmark of pseudoscience.”