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An 18-year-old French woman is in remission from HIV - despite not having taken any drugs against the virus for 12 years.

Doctors have presented the details of her case at an International Aids Society (IAS) conference in Vancouver.

It is the world's first report of long-term remission from HIV in a child.

Experts say big studies are needed to determine why some patients can continue to control the virus after stopping treatment.

The woman was born in 1996, and was passed HIV by her mother - either towards the end of the pregnancy or during childbirth.

Aged three months, she was given four anti-retroviral drugs.

But her family decided to stop the treatment when she was almost six years old.

Twelve years later, the virus levels in her bloodstream are too low to be measured - although doctors have cautioned that this could change.

This is strong evidence yet again of the powerful benefits of starting HIV treatment as early as possible. Prof Sharon Lewin, Melbourne University

Dr Asier Saez-Cirion, from the Institut Pasteur, in Paris, said: "It's likely that this girl has been in virological remission for so long because she received a combination of anti-retrovirals very soon after infection.

"With this first, highly documented case of this young woman, we provide the proof of concept that long-term remission is possible in children, as in adults.

"However, these cases are still very rare.

"The woman is living normally. Her case is unique but had gone unnoticed, even among clinicians in France."

Two years ago, a young girl in America - who became known as the "Mississippi baby" - appeared to be free of HIV.

But her remission lasted for just over two years after drug treatment was stopped.

Dr Saez-Cirion has also led research into a group of 14 adult patients known as the Visconti cohort.

They also had no signs of the virus re-emerging, despite stopping medicine. One of the patients has had the virus under control for more than 13 years.

'Inspiring'

Prof Sharon Lewin, from the University of Melbourne, in Australia, said: "The French teenager case provides strong evidence yet again of the powerful benefits of starting anti-HIV treatment as early as possible.

"This is an inspiring story for those of us working in this field, and for everyone living with HIV."

Prof Lewin added: "Important though this case is, I strongly believe that to advance our efforts towards finding a cure for HIV, we need large prospective studies that can nail down who might be able to safely stop anti-viral therapy and keep the virus under control.

"A single case report is unable to do that.

"We need to identify a robust test to measure very low levels of virus or find a better way to predict this idea of post-treatment control.

"If we had such a test, this would really help move clinical trials in the HIV cure field forward."

The French virologist Francoise Barre-Sinoussi, who won the Nobel Prize for identifying HIV, also backed the idea of large studies.

She told BBC News: "We need to try to find other such cases - and find out their markers, to see whether we can predict remission.

"The case of the Mississippi baby was of course very disappointing for the child and her family.

"But we learn as much from the negative as well as the positive data. It shows that the science around HIV is maturing."