A French teenager's HIV infection is still in remission more than 11 years after her medications were discontinued, the longest hiatus on record for a young person and the best indication yet that long-term interruption of the infection is possible in children, a researcher revealed on Monday.

The virus has been undetectable in the teenager's blood since she was 21 months old, according to the information presented on Monday at the 2015 International AIDS Society conference in Vancouver, B.C. She is now older than 18 years old and has not received anti-HIV medication since she was almost 6. A blood test shortly before her seventh birthday showed no presence of the virus.

Asier Sáez-Cirión, an assistant professor at the Pasteur Institute in Paris who conducted the research, was quick to note that the unidentified teen is not cured of HIV infection and that experts are not sure what caused her lengthy remission. "This girl is in remission," Sáez-Cirión said in an interview. "She's not cured."

Nevertheless, the case presents a number of possibilities for researchers seeking further progress against HIV, said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health.

"There's no measurable immunological reason why the (teen) is controlling" the virus, Fauci said. "But the (teen) is obviously controlling it."

In 2013, doctors reported that they had achieved a "functional cure" for the HIV infection in a Mississippi girl who was put on anti-retroviral therapy within hours of her birth. But in July 2014 — 27 months after her aggressive treatment ended — her doctors announced that she had tested positive for HIV, a setback for researchers seeking to cure a disease that affects 35 million people around the world.

A very small number of adults infected with HIV have been known to live many years without detectable levels of the virus in their blood despite ceasing treatment. Known as "elite controllers," they have been studied in an effort to determine how they naturally keep their viral loads in check. In children, such a response is even more rare.

Steven Deeks, a professor of medicine at the University of California at San Francisco, said further research must rule out the possibility that the teen is an elite controller, determine the mechanism of control and try to predict who might benefit from the same approach.

Like the Mississippi child, the French teen was treated aggressively with anti-retroviral medication shortly after she was born to an HIV-infected mother whose illness was not controlled.

In this case, the girl was given the drug zidovudine as a preventive measure for six weeks after birth, when treatment was suspended. The virus was first detected in her blood at the age of four weeks, and her viral load peaked at three months, when she began receiving a regimen of four drugs.

Shortly before she turned 6, her family discontinued the combination therapy. A year later, she was tested again, and no virus was detected in her blood. A decision was made not to resume the medication.

Sáez-Cirión noted the interruption in the girl's treatment between six weeks and three months of age. Perhaps that allowed her to develop some kind of immunity, Sáez-Cirión said.

But if that's true, Fauci noted, evidence of an immune response is not showing up in her blood tests.

Fauci pointed out that the child's combination treatment began at three months "during what would be the functional equivalent of an acute infection," when her viral load was very high. He wondered whether that timing helped her develop protection from the virus.

Sáez-Cirión said he learned of the teen's case after following the announcement of the Mississippi child's remission.

There is no way to predict the length of the teen's remission, Sáez-Cirión said. She very well may live a normal life span, he said, but as she ages, her immune system is likely to weaken.

"Once people have been in remission for a couple of years, chances . . . are going to be higher," he said.

By Lenny Bernstein