South Africa begins a major clinical trial of an experimental vaccine against AIDS, which scientists hope could be the "final nail in the coffin" for the disease.
More than 30 years of efforts to develop an effective vaccine for HIV have not borne fruit, but for the first time since the virus was identified in 1983, scientists think they have found a promising candidate.
The new study, known as HVTN 702, will involve more than 5,400 sexually active men and women aged 18-35 in 15 areas around South Africa over four years.
It is one of the biggest clinical trials involving the disease ever undertaken and has revived hopes in the scientific community of a breakthrough in the battle against AIDS.
"If deployed alongside our current armoury of proven HIV prevention tools, a safe and effective vaccine could be the final nail in the coffin for HIV," said Anthony Fauci, director of the US National institute for Allergies and Infectious Diseases (NIAID), which is taking part in the study.
"Even a moderately effective vaccine would significantly decrease the burden of HIV disease over time in countries and populations with high rates of HIV infection, such as South Africa."
South Africa was not chosen by accident for the trial. The country has one of the highest rates of HIV infection in the world -- 19.2 per cent according to the UN AIDS agency, or more than seven million people living with the virus.
Each year some two and a half million people around the world are infected with HIV, which has killed more than 30 million people since the 1980s, according to a study presented at a conference in South Africa in July.
The vaccine has been adapted for the HIV strain prevalent in southern Africa from one used in a trial of 16,000 people in Thailand in 2009, which reduced the risk of infection by over 30 percent three and a half years after the first vaccination.
The safety of the "South African" vaccine has already been tested successfully over 18 months on 252 volunteers. The new study aims to test its effectiveness.
"The results obtained in Thailand are not good enough for a roll-out (...) we have set the minimum bar at 50 percent," Lynn Morris, head of the HIV virology section at South Africa's National Institute for Communicable Disease (NICD), told AFP.
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