His contributions to microbicides for HIV prevention spans two decades and culminated in the CAPRISA 004 tenofovir gel trial which provided proof-of-concept that antiretroviral drugs can prevent sexually transmitted HIV infection and herpes simplex virus type 2 in women. He is co-inventor on patents which have been used in several HIV vaccine candidates and his clinical research on TB-HIV treatment has shaped international guidelines on the clinical management of co-infected patients.