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CIAO DATE: 03/01
Foreign Policy
Vaccinating Against Crisis
Kennet Hill
The United Nations estimates that more than 25 million Africans are infected with HIV, and more than 2 million died of HIV-related diseases in 2000. In eight countries, more than 15 percent of the adult population is infected; in the absence of effective treatment, one third of 15-year-olds in these countries will die of HIV-related diseases. Policy responses to the burgeoning epidemic have focused on behavioral change, either reducing the number of sexual partners people have or encouraging the use of condoms. But there may be another way.
Despite almost universal knowledge in many African countries of how HIV is spread and some success in reducing the number of partners people accumulate, use of condoms is still rare. Writing in the New England Journal of Medicine, T.C. Quinn and eight coauthors report that in a rural district of southwest Uganda, the number of women who say they use condoms increased only from 4 to 7 percent, and the number of men from 10 to 17 percent, both over a four-year period.
That paper, and another in Science by D.H. Barouch and some 28 coauthors, suggests a possible new approach to slowing the spread of HIV. Focusing on heterosexually transmitted HIV, Quinn and company find that among 415 discordant couples (meaning one partner is HIV-positive, one is HIV-negative), the chief predictor of whether the HIV-1 virus will spread to the healthy partner is the viral load of the infected partner–how much of the virus is in his or her system. There were no instances of transmission when the infected partner's viral load measured less than 1,500 copies of the virus per milliliter of blood. (The average among the infected was about 12,600 copies per milliliter.) Other significant factors lowering the odds of transmission included age–older people had lower risks both of infecting a partner and of being infected by a partner–and circumcision. These findings suggest that reducing the viral load in HIV-positive people will reduce, and possibly eliminate, transmission of the virus without any change in behavior.
Combination therapy, a cocktail of antiretrovirals including at least one protease inhibitor, is known to reduce viral loads to undetectable levels. But a reservoir of the virus persists in a latent state more or less indefinitely, ready to reappear if treatment is suspended. Thus, though drug treatment might reduce a patient's viral load to the point at which transmission would be very unlikely, the treatment regimen for entire societies would require a huge investment and high compliance, neither of which seems feasible right now in Africa. A more promising, though still distant, possibility is vaccination. The very high mutation rate of HIV-1 and its ability to persist in a latent state make the task of developing a vaccine to prevent HIV infection almost impossible. However, Barouch and his coauthors demonstrate the effectiveness of a post-infection vaccine in controlling viral load, if not eliminating the virus completely, thereby reducing the chances of heterosexual transmission to almost zero.
In the countries of sub-Saharan Africa, which lack the infrastructure and the resources to implement effective antiretroviral drug therapy, the development of such a vaccine may offer an affordable and effective way to control the AIDS epidemic. Of course, serious questions remain, such as whether humans will respond to the vaccine as well as monkeys have in early tests. And developing the vaccine will be a time-consuming task. The good news for Africa, though, and for other developing regions facing the AIDS epidemic, is that at last there is hope for a cheap way to fight back.
Kenneth Hill is director of the Population Center at Johns Hopkins University.