By Warren Tong

Almost 90% of women in an open-label study used a monthly HIV prevention vaginal ring at least some of the time, according to interim study results presented at CROI 2018 in Boston. Moreover, among those who used the ring, the HIV infection rate was about half of what would be expected without the ring.

The HIV Open Label Extension (HOPE) study launched in 2016, after results from the initial HIV vaginal ring study, known as ASPIRE, disappointed with a modest 27% reduction in HIV transmissions among study participants. However, when looking closer into the data, for women who used the ring most or all of the time, HIV risk reduction was at least 56%.

The vaginal ring contains dapivirine, an antiretroviral drug, which gradually releases from the ring as women wear it over the course of a month. The gradual release of dapivirine helps prevent HIV transmission, particularly in the absence of using a condom or pre-exposure prophylaxis (PrEP).

“Our interim analysis suggests that women in the HOPE study are choosing to use the dapivirine ring at least some of the time now that they know it can safely reduce their risk of HIV infection, and this is helping them achieve a level of protection,” said lead study investigator Jared Baeten, M.D., Ph.D., in a statement.

The HOPE study followed 1,407 women (representing about 57% of the women who had remained HIV negative after completing ASPIRE) from 14 study sites across Malawi, South Africa, Uganda, and Zimbabwe. The median age was 31 years, with 13% between ages 20–24 and 28% between ages 25–29. About 16% of the study’s participants had a curable sexually transmitted infection (STI). About 53% reported being married and 44% reported using a condom during their last sex act.

Ring Uptake

Of the 1,407 women, 1,299 (92%) initially accepted the vaginal ring. During follow-up, most women continued to accept the ring. They were given one ring at a time for the first three months, but then a three-month supply after three, six and nine months. The ring acceptance rate was:

90% at month 1

89% at month 2

87% at month 3

86% at month 6

81% at month 9

Ring Adherence

Rings were returned at follow-up visits. The returned rings were then tested for residual levels of dapivirine. Lower levels of dapivirine in the returned rings suggested that the ring was being used at least some of the time. Each ring is manufactured with about 25 mg of dapivirine and releases about 4 mg of dapivirine with a month of continuous use. The researchers defined returned rings with less than 23.5 mg of dapivirine as showing at least some adherence during the month. However, this did not necessarily mean consistent use.

Nevertheless, 89% of returned rings showed levels of dapivirine that indicated at least some use during the previous month, compared with 77% of returned rings showing at least some use in the ASPIRE study.

“If you think about the structure of the global pandemic, there are huge parts of the world where women are most at risk and most vulnerable, particularly young women, so it’s important that we provide them with tools that fit into their lives that can be used by them to protect themselves from HIV infection. And the ring is a good step forward in that way,” Carl Dieffenbach, Ph.D., said in an interview.

The researchers observed a total of 12 HIV infections over 616 person-years of follow-up, which translated to 1.9 infections per 100 person-years. Using a mathematical model, the researchers estimated that without access to the vaginal ring this rate would be 4.1 per 100 person-years.  

The researchers also estimated what the HIV infection rate would have been if the women had used oral PrEP instead, predicting about 2.0 infections per 100 person-years, which is similar to the vaginal ring’s interim results.

The HOPE study had a few limitations. Because this was an open-label study, there was no placebo or control group, so the researchers had to estimate what data from a control group would have looked like. Second, all the women had already participated in the ASPIRE study, so perhaps they already had lower HIV risk than expected.

The interim results provide a promising picture of what could be another HIV prevention option, particularly for vulnerable women who may not have access to other prevention methods.

The HOPE study’s final results are set to come in 2019.