Presenting at the 19th International Aids Conference in Washington DC this week, a team of clinical investigators spoke on two new clinical trials that could confirm whether a silicon vaginal ring, filled with the antiretroviral drug dapirivine, could prevent HIV infection in women. Previous studies have already shown the ring to be safe.
The two parallel studies, respectively run by the International Partnership for Microbicides, and the Microbicide Trials Network, plan to enrol over 5 000 women across Africa. As of April, sites are open in South Africa, with trials taking place in Cape Town, the Northwest province, KwaZulu-Natal and Johannesburg; Rwandan and Ugandan participants are expected to be enrolled soon.
The trials are expected to end in 2015. If the device proved to be effective in helping to prevent HIV infection, evidence will be submitted to regulatory authorities such as the US Food and Drug Administration and the Medicines Control Council for approval.
The ring is modelled on those widely used for contraception across Europe and America. Once inserted, the ring stays in place for a month, and slowly releases the dapivirine into the vaginal tissue.
"We're hoping for a very substantial degree of HIV protection for women," said Jared Baeten of the University of Washington, who is leading the Microbicide Trials Network study. "We're certainly hoping that it will provide substantial protection of at least 60%, if not higher."
Noting that poor adherence may have contributed to poor results in studies in which daily-applied antiretroviral gel was tried as a form of HIV prevention, investigators say the once-monthly feature of the ring is critical.
"A lot of women have expressed difficulty in using gels which are supposed to be used every day," said Saidi Kapiga of the London School of Hygiene and Tropical Medicine. "A lot of women are saying '[the ring] is a better product.'" Participants in earlier trials found the ring easy to insert and to remove.
Zeda Rosenberg of International Partnership for Microbicides hopes the ring can work for even longer. "A month is an easy thing to remember, however to drive down costs it could be very nice if the ring could be used for two months or three months or even more. There are trials that are being done to see if the dapivirine will last longer than a month."
This is not the first time an antiretroviral medicine—used to treat HIV—has been considered to prevent transmission of the virus. Earlier this month, oral tenofovir, marketed as Truvada, was approved by the Federal Drug Administration for use in preventing HIV infection. A vaginal gel which contains tenofovir has also been developed, but while initial studies showed nearly 40% reduction in HIV infection, follow-up trials were cut short because the gel was found to be ineffective.
In addition to the dapivirine ring, other studies are being done to consider the safety and efficacy of vaginal rings filled with other anti-retrovirals, including tenofovir and maraviroc.
There is concern that using HIV medication for prevention could increase the risk of resistance, making the drugs less effective if a person does become infected. Some doctors working in low-resource areas also say that the focus should be on expanding access to treatment for those already HIV positive, rather than using anti-retrovirals for prevention.
But with 2.7-million people infected in 2010 alone, doctors, researchers, and those at risk of contracting HIV are looking for a diverse array of prevention options.
"Given the elevated risk for HIV that women face, it's critical that we give them a range of products," said Rosenberg.
Linda-Gail Bekker of the University of Cape Town said that prevention options for women are essential because the HIV epidemic is "feminised" within South Africa. "I'm excited, I've been holding out for this moment … I think this is a milestone."