Researchers are reporting that injections of long-lasting AIDS drugs protected monkeys for weeks against infection — a finding that could lead to a major breakthrough in preventing the disease in humans.
Two studies by different laboratory groups each found 100 percent protection in monkeys that got monthly injections of antiretroviral drugs, and there was evidence that a single shot every three months might work just as well.
If the findings can be replicated in humans, they have the potential to overcome a major problem in AIDS prevention: that many people fail to take their antiretroviral pills regularly. A preliminary human trial is to start late this year, said Dr. Wafaa El-Sadr, an AIDS specialist at Columbia University’s Mailman School of Public Health, but a larger trial that could lead to a treatment in humans may still be some years away.
It has been known since 2010 that healthy people taking a small daily dose of antiretroviral drugs — a procedure known as preexposure prophylaxis, or PreP — can achieve better than 90 percent protection against infection.
But in several clinical trials since then in gay men, in intravenous drug users, and in couples where one partner is infected, it has been shown that the only participants protected were those who took their pills every day without fail. Many did not. The failure rate was particularly acute among women in Africa. Although some participants in one PreP study told researchers they were scared by rumors about side effects, many also said they were afraid to keep the pills in their home for fear that their sexual partner or a neighbor would see them and mistakenly assume they already had the disease.
An intramuscular injection that a woman could get every three months could change all that, several AIDS experts said.
In Africa, many women receive shots of long-lasting birth control hormones like DepoProvera.
About the injection protocol tested in monkeys, Dr. David Ho, director of the Aaron Diamond AIDS Research Center at Rockefeller University and an author of one of the studies, said the popularity of DepoProvera was “a good analogy for how it might work in developing countries.”
The studies were presented in Boston Tuesday at the annual Conference on Retroviruses and Opportunistic Infections.
Mitchell J. Warren, executive director of AVAC, an organization lobbying for AIDS prevention and treatment, said a long-acting injectable drug was “clearly the place to go because adherence has been the Achilles’ heel of PreP.”