Purpose of review: There have been over 30 HIV-prevention trials of which only four reported evidence of efficacy. The reasons for these negative findings may be due to ineffective interventions, but in part reflect the inappropriate selection of study populations and epidemiologic settings.
Recent findings: Three trials showed that male circumcision reduces HIV acquisition in men by 50–60%. In contrast, seven out of eight trials of bacterial and viral sexually transmitted infection (STI) control, and multiple microbicide trials show no efficacy for HIV prevention. Several microbicide trials found vaginal irritation and microulceration, which may increase HIV risk. Three vaccine trials failed to show efficacy and one trial suggested increased HIV risk in a subgroup of uncircumcised men.
Summary: The failure of most prevention trials reflects inadequate pretrial screening of potentially efficacious interventions, insufficient information on background HIV incidence, selection of high-risk populations with poor compliance and lack of generalizability, and treatment interruption during pregnancy all of which compromise power.