In 2003, Norman Hearst and Sanny Chen of the University of California conducted a condom effectiveness study for the United Nations' AIDS program and found no evidence of condoms working as a primary HIV-prevention measure in Africa. UNAIDS quietly disowned the study. (The authors eventually managed to publish their findings in the quarterly Studies in Family Planning.) Since then, major articles in other peer-reviewed journals such as the Lancet, Science and BMJ have confirmed that condoms have not worked as a primary intervention in the population-wide epidemics of Africa. In a 2008 article in Science called "Reassessing HIV Prevention" 10 AIDS experts concluded that "consistent condom use has not reached a sufficiently high level, even after many years of widespread and often aggressive promotion, to produce a measurable slowing of new infections in the generalized epidemics of Sub-Saharan Africa."
Let me quickly add that condom promotion has worked in countries such as Thailand and Cambodia, where most HIV is transmitted through commercial sex and where it has been possible to enforce a 100 percent condom use policy in brothels (but not outside of them). In theory, condom promotions ought to work everywhere. And intuitively, some condom use ought to be better than no use. But that's not what the research in Africa shows.
One reason is "risk compensation." That is, when people think they're made safe by using condoms at least some of the time, they actually engage in riskier sex.
Another factor is that people seldom use condoms in steady relationships because doing so would imply a lack of trust. (And if condom use rates go up, it's possible we are seeing an increase of casual or commercial sex.) However, it's those ongoing relationships that drive Africa's worst epidemics. In these, most HIV infections are found in general populations, not in high-risk groups such as sex workers, gay men or persons who inject drugs. And in significant proportions of African populations, people have two or more regular sex partners who overlap in time. In Botswana, which has one of the world's highest HIV rates, 43 percent of men and 17 percent of women surveyed had two or more regular sex partners in the previous year.
These ongoing multiple concurrent sex partnerships resemble a giant, invisible web of relationships through which HIV/AIDS spreads. A study in Malawi showed that even though the average number of sexual partners was only slightly over two, fully two-thirds of this population was interconnected through such networks of overlapping, ongoing relationships.