But it turns out it's not that simple - and maybe not even a first.

The 9-year-old girl, Hannah Poling, had an underlying condition that may have been worsened, triggering her autismlike symptoms.

Her parents believe it was the five simultaneous vaccines she got as a toddler in one day eight years ago that did it. Government scientists say something like a fever or infection could have set off the problem - but they didn't rule out the vaccines either.

This week, federal officials said they agreed to pay the Polings from a fund that compensates people injured by vaccines. The amount is not yet determined.

Faced with a vocal movement of parents who blamed vaccinations for their children's autism, public-health officials and major medical groups have all consistently maintained over the years that vaccines are safe.

Julie Gerberding, head of the Centers for Disease Control and Prevention, said there was no change in that position. "Nothing in any of this is going to change any of our recommendations" about the importance of vaccines, she said. "Our message to parents is that immunization is lifesaving."

And in their first appearance since their case became public, Jon and Terry Poling of Athens, Ga., acknowledged their legal case never got to the point where evidence was argued.

They nevertheless called on the government to remove thimerosal from all flu shots. Although mainstream medical research has never linked the mercury-based vaccine preservative to autism, it was removed several years ago from other shots for children.

While parents and advocates for autistic children say the case is a landmark legal precedent that signals the government is finally conceding potential autism-related risks from childhood vaccines, federal officials are saying it's nothing of the kind.

Hannah is "not a typical autistic child," said Paul Offit, chief of infectious diseases at Children's Hospital of Philadelphia and a longtime government vaccine adviser. "It's not a precedent-setting case."

Offit's comments came after the Polings held a news conference Thursday to talk about their daughter. There and later on CNN's Larry King Live, the Polings said Hannah was a bright, normal-behaving child until she got five shots at about 18 months of age. She was a little behind on her vaccinations, so the decision was made to give them all at once.

Almost immediately after, she was screaming, feverish and irritable. Then her behavior gradually changed so she would stare at fans and lights and run in circles.

"It wasn't like a switch being turned off," said Jon Poling, 37, a neurologist. "It was more like a dimmer switch being turned down."

The family filed a claim with the federal vaccine-compensation program in 2002. The government ultimately decided to concede before any evidentiary hearing.

The case might not be a first, said Gary Golkiewicz, chief special master for the U.S. Court of Federal Claims. He oversees the "vaccine court," which rules on requests for payments from the vaccine-injury fund.

"Years ago, actually, I had a case, before we understood or knew the implications of autism, that the vaccine injured the child's brain and caused an encephalopathy," he said. The symptoms that come with that, he said, "fall within the broad rubric of autism."

And there are other somewhat similar cases, he said, that were decided before autism and its symptoms were more clearly defined.

Hannah has a disorder involving her mitochondria, the energy factories of cells. The disorder, which can be present at birth or acquired later, impairs cells' ability to use nutrients. It often causes problems in brain functioning and can lead to delays in walking and talking.

The Polings were exploring two theories to explain what happened to Hannah. One is that she was born with the mitochondria disorder and the vaccines caused a stress to her body that worsened it. The other is that the vaccine ingredient thimerosal caused the mitochondrial dysfunction, Jon Poling said.

CDC officials declined to talk about the Poling case in detail, but said it should not be used to draw conclusions about risks for other children.

Scientists believe that in cases in which a mitochondrial disorder causes a child's brain function to deteriorate, the condition exists and then is worsened by a fever, infection or other stress.

And researchers don't know if a vaccination - independent of fever or infection - can cause such a stress, said pediatric neurologist Edwin Trevathan, who heads the CDC's birth-defects center.

"Most children with autism do not seem to have a mitochondrial problem, so this association," said Trevathan, "is probably relatively rare."