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Vaginal rings containing antiretroviral moderately effective in preventing HIV – but not in the youngest women
Gus Cairns, 2016-02-22 20:10:00

The results of two studies announced today at the annual Conference on Retroviruses and Opportunistic Infections (CROI 2016) in Boston, USA, show that vaginal rings impregnated with an anti-HIV drug are effective at cutting the HIV infection rate in women. However, the overall effectiveness seen was only moderate, preventing less than a third of infections – and the primary reason for this was that the rings had no effect at all in the youngest trial participants, aged 18-21 – who also had the highest rates of HIV infection. The rings were more effective in older women with almost two-thirds of infections prevented in women over 25 in ASPIRE.

Researchers are still teasing out why the vaginal rings did not work for the youngest women. Some of the low effectiveness seen was undoubtedly due to poor adherence but drug level tests did not suggest adherence rates so low as to produce zero effectiveness. The results could be caused by a combination of intrinsic efficacy of less than 100% in the rings, intermittent use among participants, and greater vulnerability to HIV infection among young women.

Whether these are the reasons, or others for the relatively low levels of adherence and lack of effect seen in young women, remains to be seen. The same is true of whether these results will be enough for the ring to be licensed as a protection method.