The U.S. government says it will pay for new tests of a drug-impregnated ring that women can use to protect themselves from the AIDS virus.
Tests of the ring showed it reduced the risk of HIV infection by 27 percent on average. But it lowered the risk of infection by 61 percent among women age 25 and older in African countries hard-hit by the virus.
It's worth finding out why the ring worked so well in older women but not at all in the youngest women, says Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which will pay for the study.
"If you could get a 61 percent efficacy in the older group, that means there is something about this that works," Fauci said.
"The real question is, in the real world, why is it not working in the younger group?" he added.
"If it had no efficacy in any age group, then you would say it was hopeless. It is very clear that this can work under certain circumstances."
Blood tests suggested the younger women had for some reason taken the ring out. The ring releases an anti-HIV drug called dapirivine and is meant to be inserted once a month and then kept in place to provide protection against sexual transmission of HIV without being obvious.
There might be something biologically different about the younger women, but if it's just behavior, Fauci said researchers need to understand why, and whether there is a way to persuade younger women to use the ring and protect themselves from HIV.
There's no vaccine against HIV, but taking just one HIV drug every day can protect people from catching the virus. The goal of the vaginal ring and other so-called microbicides is to provide women and, in some cases, men, with a variety of ways to protect themselves.
Fauci suspects some of the women volunteered for the study because they knew that being in a medical study gets them a lot of attention and care, and they weren't really interested in trying the ring. Now that the study shows it can work, if used consistently, they might be more likely to use it correctly.
"Sometimes people come into studies because they like the advantage of being in a study but they don't want to do the intervention," he said.
So the women who originally took part in the study will be invited to come back and try again. This time, they'll be told whether they are getting the drug. NIAID hopes that will give doctors a better idea of whether the ring can work.
The human immunodeficiency virus (HIV) that causes AIDS infects 36.9 million people around the world, according to the United Nations AIDS agency UNAIDS. Two million people are infected every year and more than a million die of AIDS. In the United States, more than 1.2 million people have HIV, and about 50,000 people are newly infected each year.