The ring itself, the dapivirine ring , was developed by the International Partnership for Microbicides , a nonprofit aimed at preventing HIV through the use of microbicides , or substances that kill viruses on contact. Like the NuvaRing for contraception, the dapivirine ring works for a month at a time, as it slowly releases the antiretroviral drug dapivirine to block HIV from reproducing in healthy cells. A dual-acting ring , which prevents HIV and pregnancy, is also in development.Both studies worked with female participants, most of whom were young, single, and were considered to be at high risk for HIV — high-risk behaviour includes having unprotected sex, sharing needles, and foregoing STI testing. These women were then given either a dapivirine ring or a placebo ring, and all received regular STI and HIV testing, along with free condoms and other advice for preventing HIV. ASPIRE , the first of the two studies, recruited 2,600 women in Malawi, South Africa, Uganda, and Zimbabwe and found that, compared to the placebo group, 27% fewer women contracted HIV in the dapivirine group. Researchers noted that women who were 25 or older were more likely to be consistent with wearing their rings, which reduced the rate of infection even more dramatically within their age group.Meanwhile, the Ring Study, which is still ongoing, has so far found that 31% fewer women developed HIV when using the dapivirine ring — among women older than 21, 37% fewer women contracted HIV. These early results, which are based on data from close to 2,000 women, aged 18 to 45 in South Africa and Uganda, were presented yesterday at the annual Conference on Retroviruses and Opportunistic Infections (CROI) in Boston.