Innovation & Technology April 1, 2010, 5:00PM EST

Will an AIDS Pill a Day Keep the Virus Away?

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The prognosis for PrEP in sub-Saharan Africa is mixed. Skeptics worry it may be too costly on a continent where 22 million people are infected and per capita income is $951, according to the World Bank. Speaking at this year's CROI in San Francisco in February, Anthony Fauci, director of the U.S. National Institute of Allergy & Infectious Diseases, expressed confidence in PrEP's science but questioned the feasibility. "If we can't get 70% of the people who are infected in low- and middle-income countries on therapy, how are we going to get people who aren't even infected on therapy?" he asked.

In afflicted African countries, finding people best suited for PrEP will be difficult, since nearly everyone who's sexually active is at risk of HIV, says Francois Venter, president of the Southern African HIV Clinicians Society. "I have this horror that we'll have an effective intervention very few people are going to use," Venter says. "I worry that there hasn't been enough focus on who's going to take these drugs."

Even in wealthy nations cost will be a concern. Giving Truvada to 100,000 at-risk gay men in the U.S. would cost more than $1 billion a year, according to the CDC's Web site. That sum covers only the cost of the pills and doesn't include marketing, HIV testing, and doctors' visits, the agency says.

Assuming PrEP could prevent 50% of infections, it would almost halve the lifetime risk of catching HIV among high-risk gay men in the U.S.—and almost triple the lifetime treatment costs, according to a simulation published in Clinical Infectious Diseases in March 2009. PrEP is "unlikely to confer sufficient benefits to justify the current costs" of Truvada in the U.S., researchers from Yale University and Harvard Medical School concluded in the study. The model assumed a drug cost of $753 a month for each patient. The costs of PrEP could be lower if studies show smaller drug doses are equally effective at preventing infections, or if the pills could be taken less frequently, such as shortly before risky sex, instead of every day, said A. David Paltiel, the study's lead author.

Also uncertain is how PrEP might affect business for drugmakers. Gilead's director for clinical affairs, Jim Rooney, says he doesn't know what the commercial implications might be. "It's going to depend upon the data," he says, as well as how health officials evaluate the information and what clinical recommendations they make.

When the first anti-retroviral drugs were approved for treatment in the U.S. in 1987, critics complained they weren't affordable in poor nations, says the CDC's Smith. Now, more than 20 years later, about 40% of those infected worldwide are getting the drugs, according to UNAIDS. Says Smith: "If PrEP is highly efficacious, and if countries and UNAIDS and WHO and other public health agencies believe that it has a role to play in reducing new HIV infections, then we will find a way to make it available."

Bennett is a reporter for Bloomberg News. Randall is a reporter for Bloomberg News in New York.