Over the past few decades, one of the most perplexing questions in global health is how to stop HIV.
There have been campaigns involving condoms, abstinence and even the circumcision of all men younger than 46. But one relatively new strategy, called treatment as prevention, is causing quite a buzz.
The idea is to give all HIV-positive people antiretroviral drugs to drive down the levels of virus in their systems so they no longer pose a threat of transmitting the disease.
Sounds good in theory, but how well does it play out in the slums of Nairobi or the townships of Johannesburg?
Two studies published in the journal Science find that, in places where HIV drugs are widely available, the risk for new HIV infections drops dramatically and overall life expectancy increases by more than a decade.
In other words, treatment as prevention isn't just a buzz word floating around health conferences but a promising strategy for stopping HIV even in a part of the world with one of the most severe AIDS epidemics.
Epidemiologists from Harvard University followed 17,000 HIV-negative South Africans for seven years in the province of KwaZulu-Natal. They found that, when more than 30 percent of HIV-positive people are on powerful anti-HIV drugs, it cuts the risk of contracting the virus by about 38 percent, compared to when less than 10 percent of those infected have treatment.
"The intention of this program [the South African government's antiretroviral drug program] is not treatment as prevention," Till Barnighausen, a health economist who contributed to the study, tells Shots. "The intention of this program is treatment for treatment, to save lives."
A true treatment-as-prevention model, Barnighausen says, would offer antiretroviral therapy to everyone who is HIV positive. But the South African government is providing medications only to the sickest of the sick.
Nevertheless, Barnighausen and his colleagues saw a sharp reduction in new HIV infections when drugs were widely available to the community.
"It is a program with all the failures and challenges of a real-life, public-sector, nurse-led program in southern Africa," Barnighausen says. "And despite these challenges, we see a strong effect of HIV treatment on HIV incidence. And that's extremely encouraging."
Infectious disease specialist Dr. Myron Cohen at the University of North Carolina, who wasn't involved in this study, calls the findings "a home run."
Cohen published a landmark report in 2011 showing that HIV treatment nearly eliminates the chance that an infected person will transmit the virus to a partner.
The current study, Cohen says, demonstrates that treatment as prevention doesn't just work at the individual level but also at the community level. And thus, the findings are hugely important for public health.
"It's teaching us something," he says. "You don't have to treat everybody to see a community benefit."
In a companion article, Barnighausen and his team found that overall life expectancy in KwaZulu-Natal rose more than 11 years since the province scaled up HIV treatment in 2004.
But even when studies like these show the broad benefits of anti-HIV medications, major challenges remain in getting drugs to the millions of Africans who need them, including the issue of who pays for these costly drugs.
Questions also remain about how sustainable these programs will be, especially given that HIV-positive patients are going to need to be on those drugs for the rest of their lives.