For years, scientists have studied whether taking AIDS drugs can help keep healthy people from becoming infected with the virus that causes the disease.
Now, after multiple studies, they say they finally have the answer: When taken properly, the drugs can accomplish this. But the challenge for public-health experts is to figure out how best to use a promising but potentially costly prevention strategy.
A study published in the Lancet online Wednesday found that an antiretroviral drug helps prevent HIV infection of the final group of people to be tested: those who inject illicit drugs. A daily dose of a tablet marketed under the brand name Viread reduced the risk of HIV infection by about 49% in the study of 2,413 intravenous drug users in Bangkok, Thailand.
The study follows examinations finding that antiretroviral drugs can help prevent HIV infection in heterosexual men and women at high risk of contracting it, as well as in gay and bisexual men. It reaches a similar conclusion to three earlier studies: the medications offer good protection to people who adhere to the drug regimen. The risk of acquiring HIV among those in the study who took the drugs properly was reduced by 74%.
"For PrEP to be effective it has to be consistently used," said Jonathan Mermin, director of the Division of HIV/AIDS Prevention at the federal Centers for Disease Control and Prevention, using the shorthand for pre-exposure prophylactic regimen. The CDC conducted the study along with the Bangkok Metropolitan Administration and the Thailand Ministry of Public Health.
"It's a pivotal study," said Robert Grant, senior investigator for the Gladstone Institutes and the University of California San Francisco and protocol chairman for the study that published the first results showing a preventive effect of PrEP.
"It's another angle to support the biological plausibility of PrEP working," said Jeanne Marrazzo, a professor of medicine at the University of Washington and a principal investigator of one of two studies examining its use in young women. Both those studies failed to find a preventive effect of PrEP, and investigators cited test subjects' poor adherence to the regimen. Dr. Marrazzo said she would like to see more data showing PrEP's effect in young, sexually active heterosexual women who live in areas with HIV incidence.
Roughly 8% of the estimated 50,000 new HIV infections a year in the U.S. are attributed to injection-drug use, occurring when infected users share needles with others, according to the CDC. But injection-drug use drives HIV epidemics in Eastern Europe and Central Asia, said Daniel Raymond, policy director for the Harm Reduction Coalition, an advocacy organization. He said he hoped the study would "re-energize the debate" about how to most effectively and cost efficiently eliminate HIV among drug users.
Now public-health experts must sort out under what circumstances people at risk should be offered a PrEP regimen, and how to best to counsel them about it and deliver it to them, Dr. Mermin said. "Now, we have to determine how to effectively deliver it and ensure it's effective in practice," he said.The agency is planning a demonstration project at four federally qualified health centers where people at risk of HIV infection will be recruited for the regimen, he said. The men and women in the Bangkok trial will all be offered the regimen as well, he said.
Questions to be addressed include how willing uninfected people would be to take a daily pill outside the confines of a clinical trial, how the cost would be covered and where they should get it—a primary-care clinic, a clinic specializing in HIV treatment or another setting, he said. Those who are on PrEP would need regular HIV tests, because if they were to become infected they would need to be put on a fuller complement of AIDS drugs, Dr. Mermin said.
More than 1,000 of the men in the study that Dr. Grant led are still on the regimen and being followed, and "they're using it very well," he Dr. Grant said. "We're very happy with what they're doing."
Write to Betsy McKay at firstname.lastname@example.org