"We must not drop our guard" on AIDS, says UNAIDS chief The head of the UN's AIDS agency says "now is not the time to drop our guard" despite a sharp rise of people living with the human immunodeficiency virus (HIV) having now slowed. At the start of a six-day conference on HIV/AIDS and sexually-transmitted diseases in Africa, Michel Sidibe, executive director of UNAIDS, says "we must act now and we must act differently"