Human trials for a new HIV vaccine will begin in August in South Africa, which has more HIV-positive citizens than any other country in the world. The trials are being conducted by HIV Vaccine Trials Network.

The study's principle researcher, Glenda Gray, says this is the first human trial of a vaccine specifically designed to protect against the strain of the disease most common in Africa.

"There are different strains of HIV in the world," she said. "The most predominate strain in Africa is sub-type C. It's very important that work is done looking at sub-type C vaccination and to see how this fits into the global picture."

An estimated 3.5 million Africans were infected with the fatal disease last year alone.

The new HIV vaccine was developed by the American biotech firm AlphaVax and uses new technology to deliver the vaccine to the human immune system. It combines part of a Venezuelan horse virus with a non-infectious gene from the HIV virus type common to South Africa. Researchers say it cannot infect a human with HIV.

The phase one trial, involving 96 people in South Africa and the United States, will test the vaccine's safety and is expected to last for about two years. Both South African testing sites, in Soweto and Durban, have been at the forefront of AIDS research in the country.

If the vaccine is proven safe, larger-scale studies would be launched to determine whether it is effective.

"This is a very good vaccine, it's well developed and it shows a lot of promise," said Glenda Gray. "What we need to see is whether the vaccine that we're testing here is the best to take into phase two or phase three. So, it's very important that a whole lot of different vaccine programs happen with a whole lot of different products.

The trial is just one of several expected to begin soon in South Africa and neighboring countries. Two other AIDS vaccine trials have been approved in South Africa and a third will begin soon in neighboring Botswana.