Justices on the US Supreme Court seemed split today as they heard arguments in a case to determine whether Wyeth, a pharmaceutical company now owned by Pfizer, should pay the family of a woman who became ill after receiving one of the company’s vaccines as a baby.

Such cases are normally heard in “Vaccine Court” – a special court established in 1986 to deal with concerns that rampant lawsuits might discourage companies from developing vaccines. Fees collected on each dose of vaccine are pooled together to fund Vaccine Court settlements, protecting manufacturers from the cost of dealing with these cases directly.

But when the Bruesewitz family’s case was dismissed in Vaccine Court, they turned to the Pennsylvania state court system and gradually worked their way up to the US Supreme Court.

It is safe to say the Bruesewitz case is being closely watched by thousands of others who may ultimately want to follow a similar path. About 5,000 claimants have filed cases in Vaccine Court asserting that childhood vaccines cause autism, Wyeth’s attorney Kathleen Sullivan said today. None of the six test cases heard thus far have been won. A Supreme Court ruling in favour of the Bruesewitz family, Sullivan argued, could unleash a flood of claimants whose cases before the Vaccine Court had been dismissed. “That is 5,000 potential claimants in state court,” she said.

The trouble began on April 1, 1992, when six-month-old Hannah Bruesewitz received her third dose of Wyeth’s Tri-Immunol vaccine against diptheria, pertussis, and tetanus. Hours later she had her first seizure. Over the next 16 days, she would have 124 more.

Bruesewitz’s health declined. She became lethargic and was developmentally delayed. Now, at the age of 18, she is unable to speak and, according to court documents, “will require a lifetime of supervision and care.”

Her family’s lawyers contend that the vaccine Bruesewitz received came from a lot linked to an unusually large number of adverse events, including two deaths and 39 emergency room visits. They also argue that Wyeth and federal regulators did not sufficiently inform the public of a newer, safer version of the vaccine under development at the time.

In 1995, the Bruesewitz family filed a petition with the Vaccine Court, but officials had eliminated “residual seizure disorder” from the table of eligible complaints just a month earlier. In December 2003, the court dismissed the family’s petition.

Much of today’s arguments centered on whether or not the Bruesewitz family fit the narrow criteria established by the 1986 National Childhood Vaccine Injury Act – the legislation that created the Vaccine Court – for taking a vaccine case into the state legal system.

Justices Roberts and Kennedy seemed particularly concerned about the impact of the case on vaccine manufacturers. The proliferation of such settlements, said Kennedy, would be “a tremendous expense.” The American Medical Association and 21 other professional organizations agreed in an amicus brief that expressed concern over whether the case could discourage the development of childhood vaccines.

Justices Sotomayor and Ginsberg, however, seemed more worried about providing sufficient incentive for vaccine manufacturers to ensure that their products are safe. “What is the motivation for manufacturers to voluntarily remove a drug that is causing harm to the public?” asked Sotomayor. “I do understand the cost of litigation…but I do think there’s a whole lot of hurdles in place before a plaintiff wins on one of these cases.”

The court’s newest member, Justice Elaine Kagan, has abstained from the decision, leaving open the possibility of a 4-4 tie.