the task of treating AIDS.
And, it is now clear, of preventing the disease as well. In September 2009, U.S. military and Thai researchers revealed that the clinical evaluation of an AIDS vaccine candidate in Thailand had proved 31% effective in preventing HIV. This was the first demonstration that a vaccine can protect people from HIV, and, though the effect was moderate, it generated considerable excitement in the field of prevention research. Next came the news, last year, that South African researchers had found that an ARV-based vaginal microbicide—a gel, in this case, devised to be lethal to HIV—reduced infections in women by 39%. Then, researchers studying the daily use of antiretroviral drugs to prevent HIV reported last November that the pre-exposure prophylaxis (PrEP) strategy could cut HIV infections in transgendered women and men who have sex with men by 42%. A second PrEP study, in women, had to be stopped when the trial’s Data Monitoring Committee advised earlier this year that it wasn’t likely to meet its desired endpoints. But that disappointment was quickly followed by an elating success. A study that examined how effectively antiretroviral therapy reduces the risk of HIV transmission in discordant couples—in which one partner is HIV positive and the other is not—found that the early and appropriate use of such drugs by the infected partner can be as much as 96% effective in preventing the sexual transmission of the virus.
Meanwhile, researchers in laboratories around the world have worked together to isolate and characterize a number of antibodies that can neutralize a broad spectrum of circulating HIV variants. Such antibodies hold vital clues to the design of a new generation of broadly effective HIV vaccine candidates, and they are today being systematically exploited for that purpose. Researchers have also made significant headway in developing new and potentially vastly more effective vaccine vectors, or vehicles for the delivery of AIDS vaccines. A recent study of a vaccine candidate built into one such vector examined its ability to protect monkeys from the simian version of HIV, known as SIV. The researchers found that while the novel SIV vaccine cannot prevent infection, it suppresses SIV so effectively in many cases that the virus eventually cannot be detected in blood and tissue samples of vaccinated monkeys using standard laboratory methods. The challenge will be translating this breakthrough in vector design into an HIV vaccine candidate that can be safely and ethically tested in humans.
After years of painstaking work, and no shortage of setbacks, we have in hand today solid proof of concept for every one of the major experimental strategies for preventing HIV. Now each of those results must be confirmed and improved upon—certainly in the case of vaccines. All this will take time and money and so, inevitably, test the patience of policymaker and advocate alike.
Prevention—especially the development of new biomedical tools for that purpose—has to be a global priority. We simply cannot treat our way out of this pandemic. Each day, 7,000 people are newly infected with HIV; for every person put on antiretrovirals, two more become HIV infected. Current prevention methods cannot stem the tide of AIDS. The only real hope we have of ending this pandemic is through the deployment of effective biomedical tools to block HIV transmission, such as vaccines. We are pleased to note that the prospects of that happening have never looked better than they do today.