With an estimated 44-million people living with HIV-AIDS, researchers say only a vaccine can halt the high rate of infection. But a successful vaccine remains years away.

Duke University's Dr. Barton Haynes is one of the conference organizers "As much as scientific research has accomplished over the last few years, much more needs to be done. Clearly, we're still far from the development of a completely protective and practical vaccine."

Salim Karim, a leading vaccine researcher at the University of Natal, says everyday without a vaccine allows the pandemic to stretch further. "In the three days that we will be in this conference, 24,000 of my fellow countrymen in South Africa will become infected with HIV."

But Dr. Karim says there is some encouraging news. He says vaccine testing has taken on a much more global hue. For example, trials are underway in Trinidad, Brazil, Botswana, Uganda, Kenya and Thailand. And more countries, such as China and India, are developing their own vaccines.

He says there are three basic reasons why it has been difficult to come up with a successful AIDS vaccine especially one that would work in developing countries. One is the who, what, when, why, where and how of the pandemic otherwise called epidemiology.

"The first is that the epidemiology of HIV is dramatically different in these settings. If you take Southern Africa, most of the people becoming infected are young and they are women. If you take just my own country in South Africa, there are twice as many women who are becoming infected with HIV as there are men."

The second problem he says is there are many different sub-types of HIV and they can vary from region to region. Finally, he says peoples' genetic make-up may determine whether a particular vaccine works for them.

The conference runs through Sunday, September 21.