The Harvard AIDS Institute has collaborated with Botswana’s Ministry of Health for five years, and Essex has traveled back and forth between the country and Boston many times, but he has never stayed so long.

"Our programs in Botswana have been steadily expanding, and with a potential vaccine trial scheduled to start later this year, I really wanted to be there," said Essex.

Mine workers from Debswana Diamond, Botswana’s largest company, are expected to join the effort. Last March, Debswana Diamond said it would begin to provide expensive HIV treatment drugs called antiretrovirals to its employees and their spouses and would pay 90 percent of the costs. One-third of the company’s employees had tested positive for HIV.

The candidate vaccines to be studied in the trial are unusual and important in that they are designed specifically for prevention against a subtype of HIV called HIV-1C. Two-thirds of all new HIV infections in the world are of the type HIV-1C, said Essex, and many of those new infections are taking place in African countries. But many current vaccine research programs focus on HIV-1B, the strain most common in Europe and North America.

"The virus strain in Botswana is clearly different from those we see in the West," said Essex. "No one knows how important that difference will be in terms of vaccine development. No one knows if a vaccine against HIV-1B will work as well against HIV-1C. That’s why it is important to make vaccines with HIV-1C in mind."

Essex and colleagues Thumbi Ndung’u and Boris Renjifo of the Harvard AIDS Institute recently announced that they have made the first infectious molecular clone of HIV-1C, which is crucial in examining the genetic characteristics of the subtype and understanding its ability to spread so rapidly in the populations of sub-Saharan Africa.

Their paper "Construction and Analysis of an Infectious Human Immunodeficency Virus Type 1 Subtype C Molecular Clone" is published in the June issue of the Journal of Virology.

They also have produced the first Simian/Human Immunodeficiency Virus (SHIV) chimera based on HIV-1C of African origin, which will allow testing of candidate vaccines in rhesus monkeys. Both developments are critical steps in designing effective vaccines to stop the spread of AIDS.

Essex will also help open a state-of-the-art HIV reference research laboratory in Gaborone by the end of this year. Currently, the Harvard AIDS Institute and the Botswana government run a small lab with a staff of seven people, but the new lab will employ between 40 and 50 people. The Botswana government will pay for the new lab while on-site training will be provided to local scientists and technicians by the Harvard AIDS Institute.

The Botswana government, headed by President Festus Mogae, is trying to stem the AIDS epidemic in the country, which has the highest HIV infection rate in the world.

More than 35 percent of adults in Botswana are infected with HIV, said Essex, while the average percentage of infection in all other African countries is 8 percent.

Said Essex, "The Botswana government has shown that it is committed to doing something about the horrendous AIDS epidemic there, and we are eager to continue to participate in the process."