Government health officials have conceded that childhood vaccines worsened a rare, underlying disorder that ultimately led to autismlike symptoms in a Georgia girl, and that she should be paid from a federal vaccine-injury fund.

Medical and legal experts say the narrow wording and circumstances probably make the case an exception, not a precedent for thousands of other pending claims.

The government “has not conceded that vaccines cause autism,” said Linda Renzi, the lawyer representing federal officials, who have consistently maintained that childhood shots are safe.

However, parents and advocates for autistic children see the case as a victory that may help certain others. Although the science on this is very limited, the girl’s disorder may be more common in autistic children than in healthy ones.

“It’s a beginning,” said Kevin Conway, a Boston lawyer representing more than 1,200 families with vaccine injury claims. “Each case is going to have to be proved on its individual merits. But it shows to me that the government has conceded that it’s biologically plausible for a vaccine to cause these injuries. They’ve never done it before.”

A lawyer for the 9-year-old girl has scheduled a news conference in Atlanta today.

Nearly 5,000 families are seeking compensation for autism or other developmental disabilities they blame on vaccines and a mercury-based preservative, thimerosal. It once was commonly used to prevent bacterial contamination but since 2001 has been used only in certain flu shots. Some cases contend that the cumulative effect of many shots given at once may have caused injuries.

The cases are before a special “vaccine court” that doles out cash from a fund Congress set up to pay people injured by vaccines and to protect makers from damages as a way to help ensure an adequate vaccine supply. The burden of proof is lighter than in a traditional court, and is based on a preponderance of evidence. Since the fund started in 1988, it has paid roughly 950 claims but none for autism.

Studies repeatedly have discounted any link between thimerosal and autism, but legal challenges continue. The issue even cropped up in the presidential campaign, with Republican Sen. John McCain asserting that “there’s strong evidence” autism is connected to the preservative.

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

Federal officials say the law bars them from discussing the case or releasing documents without the family’s permission. However, the Associated Press obtained a copy of the concession by U.S. Department of Health and Human Services officials.

According to the document, five vaccines the girl received on one day in 2000 aggravated her mitochondrial condition, predisposing her to metabolic problems that manifested as worsening brain function “with features of autism spectrum disorder.” In the 1990s, the definition of autism was expanded to take in a group of milder, related conditions, which are known as autism spectrum disorders.

The document does not address whether it was the thimerosal or something else entirely in the vaccines that was at fault.