Washington, Nov 29 (IANS): The first HIV vaccine efficacy study in seven years has begun in South Africa to test whether a modified vaccine candidate can provide effective protection against the AIDS virus, the US National Institutes of Health said.

The study -- called HVTN 702 -- aims to enroll 5,400 sexually active men and women aged 18 to 35 years, making it the largest and most advanced HIV vaccine clinical trial to take place in South Africa, Xinhua news agency reported.

"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 Director of the National Institute of Allergy and Infectious Diseases (NIAID), Anthony Fauci in a statement.

The experimental vaccine regimen being tested in HVTN 702 is based on the one investigated in the RV144 clinical trial in Thailand that was found to be 31.2 per cent effective at preventing HIV infection over the 3.5-year follow-up after vaccination.

The new trial, to be conducted at 15 sites across South Africa, where more than 1,000 people become infected with HIV every day, aims to test whether it will provide greater and more sustained protection than the RV144 regimen.

Volunteers will been randomly assigned to receive either the investigational vaccine regimen or a placebo. All participants will receive a total of five injections over one year, and results are expected in late 2020.

"If an HIV vaccine were found to work in South Africa, it could dramatically alter the course of the pandemic," said HVTN 702 Protocol Chair and President of the South African Medical Research Council Glenda Gray.