The NIH-funded Aspire study, on the other hand, tested on 2,629 women in sub-Saharan Africa. Its researchers found 27 percent fewer cases of HIV infection in those who received the dapivirine rings compared to those who were given placebos. But when they only included women over 25 in the count, they found that the ring reduced the rate of infection by 61 percent. That becomes 56 percent for everyone over 21.

The overall percentage is much lower, because it provided no protection for women aged 18 to 21. It could be because they didn't use the ring as frequently as the older women did. The dapivirine ring needs to be replaced every month, see, and not everyone came back regularly. Also, it has to be used all the time to work. The researchers plan to look into it more anyway, in case there's a biological reason why it wasn't as effective on younger women.

The Ring Study's Dr. Zeda Rosenberg is positive her team can apply for approval from South African and European regulators next year. She says they can even release multi-purpose rings: they can make a variant that also comes with birth-control drugs, for instance. Still, the percentages the groups presented are rather low. Scientists have to conduct further studies and figure out how to make the ring more effective before it's released to the public.