Carolyn Williamson, University of Cape Town Robert Johnston, University of North Carolina Michelle Galloway, Medical Research Council, SA Why a vaccine? It's 20 years since the first evidence of acquired immune deficiency syndrome (AIDS) and the discovery of the virus that causes this clinical syndrome, the human immunodeficiency virus (HIV). Since then, over 60 million people have become infected, 40 million of whom are currently living with HIV - 70% of them in Africa.