The latest tool for preventing HIV in women will be familiar to anyone who has used a NuvaRing for contraception, or an estrogen-replacement ring to treat symptoms of menopause.

Like those devices, the dapivirine ring is inserted into the vagina and worn round-the-clock.

But instead of hormones, the ring steadily secretes dapivirine, an antiretroviral (ARV) drug that interferes with the ability of HIV to replicate itself.

hiv in women

In a person newly exposed to HIV, dapivirine can prevent the virus from getting a foothold in the body.

“That’s the key to prophylaxis against HIV … having the drug there when the exposure happens,” Dr. Jared Baeten, Ph.D., a University of Washington School of Public Health professor, who helped design a clinical trial of the ring through the Microbicide Trials Network (MTN), told Healthline. “Then when someone has sex with someone with HIV, the drug is already there so that the virus immediately comes into contact with the medication.”

Read more: The underreported epidemic of HIV among U.S. women »

Testing the ring

So far, the ring has been tested in large clinical studies in Malawi, Uganda, South Africa, and Zimbabwe.

The MTN-sponsored study, known as A Study to Prevent Infection with a Ring for Extended Use (ASPIRE) took place between 2012 and 2015.

It involved more than 2,600 women. All of them were counseled on sexual health, given condoms, and assigned an experimental intravaginal ring. For half the women, the ring contained dapivirine. The other half was given a placebo ring.

The results suggest that the ring is effective when used consistently. Young women were unlikely to use the ring as directed, which meant it offered no protection. However, older women had their incidence of infection cut by half, and the women who used it most consistently were protected at a rate of more than 75 percent.

That’s a disparity that needs to be addressed, Rowena Johnston, Ph.D., vice president of the AIDS research agency amfAR, told Healthline.

“We know that antiretroviral therapy can decrease the risk of acquiring HIV,” she said. “So I think the real challenge is working out how do we deliver that to women such that this is a product that they can and will use to protect themselves from HIV.”

Adherence to prevention tools, whether they are pills, creams, or condoms, has always been an issue confronted by those trying to combat HIV.

A daily pill — such as the pre-exposure prophylaxis (PrEP) drug Truvada — doesn’t work for everyone.

Neither does a messy cream that has to be applied before sex.

And many women are unable to ask their partner to use condoms.

“All along we were following this and thinking, is there something that’s longer acting, that’s not messy, and that women can use more discreetly and wouldn’t interfere with the sex act?” Zeda Rosenberg Sc.D., chief executive officer of the International Partnership for Microbicides (IPM), which developed the ring, told Healthline.

Read more: New target found for potential HIV vaccine »

Convincing women to use it

The nonprofit organization designed the ring to be as nonintrusive as possible. It only needs to be changed once a month and can go unnoticed by a woman’s sexual partner.

Rosenberg is not dismayed by the fact that not all women in the study used the ring.

“In a clinical trial setting, women are told every time they come to the clinic we don’t know whether this product works, and we don’t know its safety in large numbers of people,” she said.

Outside a clinical trial, patients’ attitudes are different.

“Once safety and efficacy of a product is known, that use tends to be higher because people then are choosing to use it rather than enrolling in a trial,” Rosenberg said.

The women who participated in ASPIRE have the option to continue in a second study where all participants are given an active ring. The same is true for a similar study conducted concurrently by IPM.

Rosenberg hopes the ring will join a variety of other options that will be affordable and accessible for women who want to reduce their chances of contracting HIV.

“So a woman will walk into a clinic one day hopefully, and if her partner will use condoms that’s what should happen. If she wants to use oral PrEP and can take a daily pill, that would be great. If she wants something that’s longer acting she could get the ring or the injection,” Rosenberg said.

Read more: How can we get people to actually use HIV prevention drugs? »

An urgent need

Finding HIV prevention tools that work for women is an urgent matter.

Worldwide, more than half of all people living with HIV are female, and the virus is the leading cause of death in women between the ages of 15 and 49.

Some of the reasons for this gender disparity are biological. But there are social explanations as well.

In many cases, women are powerless to request that their partners use condoms. They may also face violence or risk being cut off financially. And condoms aren’t a good option for women trying to start a family.

The prognosis for a person diagnosed with HIV today is better than it was at the start of the AIDS epidemic, so long as they have access to ARV drugs.

But that doesn’t mean we should turn our attention away from prevention, Baeten said.

“We are overwhelmed every year by hundreds and hundreds of thousands of people getting infected with HIV worldwide,” he said. “Those individuals become a growing burden for treatment need, a growing burden for additional prevention need, and if a cure were to be developed, a burden for cure as well. So if we can turn off new infections we can then focus our best efforts on making sure that we turn the tide on the HIV epidemic.”