Objective Two randomised controlled trials showed that pre-exposure prophylaxis (PrEP) reduces HIV transmission between heterosexual men and women. We model the potential impact on transmission and cost-effectiveness of providing PrEP in sub-Saharan Africa.

Methods We use a deterministic, compartmental model of HIV transmission to evaluate the potential of a 5-year PrEP intervention targeting the adult population of 42 sub-Saharan African countries. We examine the incremental impact of adding PrEP at pre-existing levels of male circumcision and antiretroviral therapy (ART). The base case assumes efficacy of 68%; adherence at 80%; country coverage at 10% of the HIV-uninfected adult population; and annual costs of PrEP and ART at US$200 and US$880 per person, respectively.

Results After 5 years, 390 000 HIV infections (95% UR 190 000 to 630 000) would be prevented, 24% of these in South Africa. HIV infections averted per 100 000 people (adult) would range from 500 in Lesotho to 10 in Somalia. Incremental cost-effectiveness would be US$5800/disability-adjusted life year (DALY) (95% UR 3100 to 13500). Cost-effectiveness would range from US$500/DALY in Lesotho to US$44 600/DALY in Eritrea.

Conclusions In a general adult population, PrEP is a high-cost intervention which will have maximum impact and be cost-effective only in countries that have high levels of HIV burden and low levels of male circumcision in the population. Hence, PrEP will likely be most effective in Southern Africa as a targeted intervention added to existing strategies to control the HIV pandemic.