This most recent trial was a small Phase I trial to ensure that the vaccine tested in Thailand was safe and tolerable for South Africans. The study enrolled 100 participants and was evenly split among men and women. More than half of the women in the study were overweight or obese.

“We know from previous studies that high body mass index, gender, age, and genetics impact HIV vaccine-induced responses. Given the rising prevalence of obesity in South Africa and the distinct differences in genetic backgrounds [from Thailand], we needed to validate whether the regimen in Thailand was immunogenic in South Africa,” said Dr. Glenda E. Gray, executive director of the Perinatal HIV Research Unit at the University of the Witwatersrand and the first woman to lead the South African Medical Research Council. Gray was also the co-principal investigator of the trial.

“We saw no significant difference in CD4 T-cell responses for body mass, gender, or age,” Gray said. “Females responded slightly better than males and young slightly better than older age groups.”

CD-4 cells—sometimes known as T4 or T-helper cells—are white blood cells that are a critical part of the human immune system. These are called “helper” cells because they send signals to activate the body’s immune response when an “intruder”—such as a virus or bacteria—is detected. HIV infection leads to a gradual reduction in these cells. The virus mutates and hides in CD-4 cell reservoirs. When these cells multiply to fight an infection, they end up making more copies of the virus. Scientists have attempted to develop a vaccine for HIV for more than three decades. But the genetic diversity of the virus and its unique ability to “replicate unrelentingly despite everything the immune system can throw at it”—in the words of Harvard University virologist Ron Desrosiers—“are among the reasons this has proven to become a extraordinary challenge.” The South African study investigated safety and immune response. It did not measure how effective the vaccine was against preventing HIV. The study found that the vaccine produced immune responses—triggered the production of CD-4 cells—in all healthy adults who received the vaccination. Sixty-eight of the 100 participants had responses that were "comparable to or better than those induced in RV144,” note researchers. The results were announced at the HIV Research for Prevention 2014 conference.

Starting in January 2015, Phase 1 and Phase 2 trials will modify the Thai regimen to make it more “friendly” to South Africa. There are up to 10 HIV subtypes—these are called “clades”—and the subtype “C” in Southern Africa is different than subtypes B and E found in Thailand. South African researchers will modify the vaccine with a Clade “C”-specific insert. Researchers will also add a protein adjuvant—sort of a “turbocharge” to increase the body’s immune response. A second vaccination—known as a “booster”–will be given at 12 months to make the regimen stronger and more durable.