Is science on the threshold of a vaccine against HIV? With the discovery in late 2012 that potent antibodies are capable of neutralizing HIV strains, the answer may be a cautious yes.

The dramatic breakthrough came in Johannesburg, South Africa, in late October 2012. Scientists found that two South African women, both infected with HIV, produced antibodies that neutralized and killed more than 90 percent of the known virus strains. This could lead to a vaccine against the deadly virus.

Worldwide, South Africa has the highest number of people infected with the AIDS virus. More than five million people, out of a total population of some 50 million in the country, are living with HIV/AIDS.

The study was conducted by the Center for the AIDS Program of Research in South Africa (CAPRISA) and involved scientists from the National Institute for Communicable Diseases (NICD)as well as from several universities in the country. Over a period of several years, blood samples from two infected women were taken at intervals. As the study progressed, the scientists noted sugar molecules on the outer protein of the virus. They discovered that the sugar molecules, called glycan, made the virus vulnerable at a specific position, which they called position 332. At this point of vulnerability, the body is able to fight back with a broadly neutralizing response. The sugar molecules caused the immune systems of both women to make antibodies that, in turn, killed most of the HIV strains. In other words, they hit a weak spot in the virus.

The fact that glycan could destroy most of the HIV strains is all-important. A cure for HIV has eluded the medical world for decades, in part simply because the virus has so many different varieties. This new antibody does not cure the disease, but it does stop the spread of the virus to healthy cells.

Scientists identified the existence of these neutralizing antibodies about three years ago. However, until this study, it was not known how the human body was able to produce them. The discovery has been called a sort of cat and mouse game between HIV itself and the immune response of the infected person.

Scientists from Harvard University and the University of North Carolina, who are among those studying HIV in the United States, have suggested that the new vulnerability site known as 332 may be present in about two-thirds of the types of virus found in South Africa. Therefore, an AIDS vaccine, if it is developed from this finding, will need to attack other targets on the virus as well.