A vaginal ring that contains an anti-HIV drug to protect women could transform the response to the AIDS epidemic, says a leading international development charity.

The International HIV/AIDS Alliance (the Alliance) welcomed results from two new trials showing that a monthly vaginal microbicide ring that provides sustained delivery of the antiretroviral drug (ARV) dapivirine reduces overall HIV infections among women by about 30%.

Divya Bajpai, senior advisor for sexual and reproductive health and rights at the Alliance said: "Women have been waiting for this. The options we currently have are just too limited. The trial results show that we can provide women with a means of protecting themselves from HIV, ways that don't require the active participation of their male partner, this is potentially groundbreaking."

For women over 21 years of age the trials showed promising levels of effectiveness. In addition, the ring is already used for contraception and could be integrated into existing sexual and reproductive health services. We also understand that efforts will be made to make the ring affordable, which is vital for women in low and middle income countries who are most affected by HIV."

The results of the trials for 18-21 year-old women were less encouraging with the ring providing 'little or no protection' probably due to lack of adherence.

"We need to explore the ring's potential for young women and adolescent girls who, crucially, are less able to negotiate condom use, an important factor driving the need for discreet and long-acting solutions like the dapivirine ring," said Ms Bajpai.

"Ultimately the potential for the ring is huge. We want every woman to have the right to choose freely which HIV prevention methods work for her."

The results are from two large Phase III clinical trials - The Ring Study and ASPIRE - of a monthly vaginal ring containing the antiretroviral drug (ARV) dapivirine. ASPIRE (MTN 020) was launched by the Microbicide Trials Network (MTN) and enrolled 2,629 women in Malawi, South Africa, Uganda and Zimbabwe, with results are expected in late 2015 or early 2016; and The Ring Study (IPM 027) was sponsored by the International Partnership for Microbicides (IPM) and enrolled 1,950 women at sites in Uganda and South Africa.

The full results will be presented at the annual Conference on Retroviruses and Opportunistic Infections (CROI) in Boston, Massachusetts on Wednesday 24 February - http://www.croiconference.org/.