Stefan Ferrari got his required vaccines before he was 18 months old. At the time, his parents said, he was a healthy, verbal boy.

But after his last round of booster shots, Stefan stopped speaking and, now 10 years old, he has not spoken since.

Stefan's parents, Marcelo and Carolyn Ferrari of Atlanta, filed suit, alleging the vaccines caused neurological damage to their young son. On Tuesday, the family's lawyer asked the Georgia Supreme Court to let the case against two vaccine manufacturers, Wyeth and GlaxoSmithKline, go forward.

Lawyer Lanny Bridgers told the court it was bad timing when Stefan received his last shots. A year later, the American Academy of Pediatrics recommended that thimerosal, a preservative used for multi-dose vaccine vials, be removed from childhood vaccines. The Ferraris contend that manufacturers should have made vaccines without thimerosal before Stefan was vaccinated.

But a lawyer arguing on behalf of the manufacturers told the state high court that the suit is barred by the 1986 National Childhood Vaccine Injury Compensation Act.

The law says no vaccine maker shall be held liable in a civil action for damages arising from an injury or death caused by vaccines given after Oct. 1, 1988.

The exceptions are if the vaccine was improperly prepared or contained improper directions or warnings. Neither of these were involved in Stefan's case, Daniel Thomasch, a lawyer for the manufacturers, told the court.

"It was the clear intent of Congress to pre-empt precisely the claims that are at issue here," he argued.

Congress passed the law after hundreds of lawsuits were filed against vaccine manufacturers. The litigation increased insurance costs, drove out some manufacturers and threatened the continued production of some vaccines, even though the lawsuits were largely unsuccessful, Thomasch said.

"It has been a remarkably successful program," he said of the 1986 law. "This wasn't a rescue of the industry. It was an important step to make sure vaccines remained available in the United States."

Seven of eight courts to consider challenges to the 1986 act have ruled in favor of the manufacturers. Last year, the Georgia Court of Appeals became the first court in the nation to rule the act did not pre-empt state law allowing such lawsuits. The manufacturers are appealing that decision to the state Supreme Court.

Bridgers, the Ferraris' lawyer, told the justices that courts should review vaccine challenges on a case-by-case basis, not bar them completely. Otherwise, complaints must be brought in Washington before the U.S. Court of Claims where there are restrictions on the amount of awards, he said.

"Did Congress really intend to create an opt-out provision that allows the child to be thrown out of court?" Bridgers asked the justices. "I think not."