Objective: To review biomedical determinants of women's vulnerability to infection with HIV and interventions to counter this, within the southern African context.

Results: Apart from number of exposures, if any, several factors influence the efficiency of HIV transmission during sex. Acute HIV infection, with extraordinarily high semen viral load, in conjunction with concurrent partnerships maximizes this efficiency. Delaying sexual debut and avoiding HIV exposure among biologically and socially vulnerable youth is critical. Reducing unintended pregnancies keeps girls in school and prevents vertical (also possibly horizontal) transmission. Female condoms, especially newer versions, are an under-exploited prevention technology. Control of sexually transmitted infections (STI), which facilitate HIV acquisition and transmission, remains important, especially among the most at-risk populations. Pathogens, such as herpes simplex virus type 2, which contribute most to HIV transmission in southern Africa must be targeted, although the importance of bacterial vaginosis and Trichomonas vaginalis is under-recognized. Also, heavy episodic alcohol use affects sexual decision-making and condom skills. Moreover, prevailing social contexts, partly a consequence of poor leadership, constrain the behavioural 'choices' available for girls and women.

Conclusions: Priority health sector interventions for preventing HIV are: male and female condom programming; prevention and control of STI; outreach to most vulnerable populations; HIV testing in all patient-provider encounters; male circumcision; and the integration of HIV prevention within sexual and reproductive health services. Future interventions during acute HIV infection and microbicides will reduce women's biological vulnerability. Far-reaching measures, such as sexual equity and alcohol control, create conditions necessary for achieving sustained prevention results. These are, however, contingent on stronger, more informed cultural and political leadership.