The first test of a daily pill to prevent HIV infection gave a tantalizing hint of success, but a real answer must await a larger study due out next year.
The experiment, done in Africa, mainly showed that the drug Viread is safe when used for prevention. Fewer people given the drug caught the AIDS virus than those given dummy pills, but so few in either group became infected that valid comparisons cannot be made, scientists said.
Still, “it’s incredibly encouraging,” said Dr. Helene Gayle, president of the antipoverty group CARE and co-chair of the International AIDS Conference in Toronto, where the results were released on Saturday.
If future studies show effectiveness, the drug “would be an incredibly important new prevention tool that we should make available as soon as possible,” she said.
A vaccine is considered the best hope for stopping the spread of AIDS, but scientists have not been able to make one that prevents infection. Condoms and counseling have not been enough – the virus spreads to 5 million more people worldwide each year.
The new approach involves Viread (known generically as tenofovir), a drug already used to treat AIDS. Animal research suggests that taking it before being exposed to HIV, through drugs or sex, could help prevent infection.
A study by Family Health International, funded by the Bill & Melinda Gates Foundation, tested it on women in Africa at high risk because of multiple sex partners (many were prostitutes). None had HIV at the start of the study. They were randomly assigned to get either daily Viread or dummy pills and all were counseled and given condoms.
No safety problems emerged – an important first step, said Leigh Peterson, project manager for Family Health. After an average of six months, only two HIV cases developed among the 427 women on Viread, compared with six infections among the 432 given the fake drug.
“We really would be irresponsible to draw conclusions at this time,” because those are too few cases to make judgments on, said Dr. Ward Cates of Family Health. “But it does underscore the importance of moving forward very quickly now on the other studies on the drawing board.”
The federal Centers for Disease Control and Prevention has studies under way in drug users in Thailand, heterosexual men and women in Botswana, and gay men in Atlanta and San Francisco. Plans are proceeding to add a third U.S. city, said Dr. Lynn Paxton, project leader at CDC.
The Thai results may be ready late next year and should reveal whether the strategy works.