They have been studying three HIV-infected men and three women who did not develop Aids symptoms over 7 to 10 years. One of the women has since died of Aids but she was receiving drugs that depressed her immune system to treat an unrelated illness.
There have been other reports of symptom-free HIV infection, but the sources of the virus have been less clear and researchers have only been able to speculate whether the lack of symptoms was because the patient's immune system was particularly strong or whether the virus was particularly weak.
The group was unusual because they were infected with the same strain of HIV from a single source. It came from the first man in the group who was diagnosed in 1984 and who had been a blood donor.
Three established tests to track the progress of HIV infection found no damage to the immune systems of people in the group.
A detailed report from the researchers in tomorrow's edition of the Lancet says that if similar symptomless groups could be found there would be new hope of understanding HIV disease.
The researchers, from the National Centre in HIV Epidemiology and Clinical Research, University of New South Wales, say study of symptomless HIV could be vital in developing vaccines.Reuse content