Dapivirine rings have previously been shown to cut HIV infections by at least 56 percent in women older than 25. Now, a study has shown that this revolutionary prevention strategy is safe to use in teenage girls, meaning it's one step closer to getting regulatory approval and being widely available.

It consists of a flexible ring, worn constantly and replaced monthly, that sits on the cervix and releases the antiretroviral drug dapivirine to fight off HIV infections.

This research, presented at the 9th IAS Conference on HIV Science, is the first time scientists have analyzed how usable, effective, and safe the prevention treatment is among teenage women and girls. This is pretty important, as adolescent girls and young women (aged 15 to 24) represent just 11 percent of the total adult population, yet in 2015 accounted for 15 to 24 percent of new HIV infections among adults globally. In sub-Saharan Africa, that figure is closer to one in four.

"If the ring is approved for women older than age 18, it's imperative that we have the data in hand to show that the ring is safe to use in younger women as well," Sharon Hillier, from the University of Pittsburgh School of Medicine, said at the conference. "HIV doesn't distinguish between a 16-year-old and an 18-year-old. Access to safe and effective HIV prevention shouldn't either. Young women of all ages deserve to be protected."

The research recruited 96 girls aged 15 to 17 from six sites across the US, 73 of which were in the dapivirine ring group and 23 were assigned to use the placebo ring. They were asked to use their ring for a month at a time for a total of six months.

Of the girls who had the dapivirine ring, 87 percent had detectable levels of the drug in their vagina, suggesting it could be as effective as shown in adult women. They found no differences in safety outcomes between the dapivirine ring and the placebo ring. They also reported that 95 percent of under 18 girls found the ring easy to use and 74 percent said they were not aware of the ring during daily activities.

This new study, known as MTN-023/IPM 030, was designed to “tick the boxes” to provide all the information that regulatory authorities would need to expand approval of the ring to include girls under the age of 18. Previous trials, involving over 4,500 female volunteers from across southern and eastern Africa, have already shown the ring to be safe and to help protect against HIV among women aged 18 to 45.

So far, it looks promising. Earlier this month, the International Partnership for Microbicide announced that the application for the ring was under review by the European Medicines Agency for use in adult women.