Announcing the "huge advance", scientists said yesterday that the "broadly neutralising antibodies" fight more than one strain of the HI virus.

It is hoped that the knowledge of how the body produces these powerful antibodies can be used to develop a vaccine that would mimic the virus and stimulate the body into making the same antibodies.

The director of the Centre for the Aids Programme of Research in Southern Africa, Professor Salim Abdool Karim, said: "Broadly neutralising antibodies are considered to be the key to making an Aids vaccine."

One of the leaders of the study, National Institute for Communicable Diseases professor Lynn Morris, said the research findings were a "major scientific advance. Infected people give us the clues on how to make a vaccine".

But she cautioned that a vaccine was still "years away".

The research was led by the National Institute for Communicable Diseases and included scientists from Caprisa, and the universities of KwaZulu-Natal and Cape Town, and Wits, in conjunction with Harvard University and the University of North Carolina.

They conducted long-term research on two HIV-positive women in KwaZulu-Natal whose bodies naturally produced the "super" antibodies.

The co-leader of the study, Dr Penny Moore, said researchers looked at the "cat-and-mouse game" being played out between the body and the virus.

They found that the virus developed a protective sugar coating when fighting the body's antibodies, but a certain type of sugar, position 332, developed a vulnerability in the virus that prompted the body to make the powerful antibodies.

Karim said one of the women in the study had since died from TB "but her legacy lives on. The other is a 43-year-old who is doing very well. She is on antiretrovirals and has a long-term partner and her viral load is undetectable."

Moore said the next step was to find evidence in similar studies around the world to collaborate the findings.

Health Minister Aaron Motsoaledi praised the scientists, calling their discovery "a great day for South Africa". He urged people not to expect a vaccine immediately.

"People still need to test for HIV once a year and use condoms."