Intarcia Therapeutics Inc. The Medici drug delivery system, a subdermal implant, could change the way people prevent the spread of HIV.

People at high risk of contracting HIV can significantly lower their chances of getting the virus with a daily pill known as PrEP, or pre-exposure prophylaxis, medicine. While this innovation has led to lower rates of new HIV cases among some, others can’t stick to the once-a-day regimen, prompting scientists to search for a low-effort, long-term way for people to take PrEP on schedule.

To help develop a long-term solution, the Bill and Melinda Gates Foundation is investing up to $140 million in the creation of a subdermal implant that can continuously release PrEP for up to one year before needing to be replaced.

The device, which is called the Medici drug delivery system, is being developed by Boston-based Intarcia Therapeutics Inc. Because strong adherence is key to effective HIV prevention, this device could be crucial in helping people stick to a regimen without having to worry about how to acquire and store pills or having to remember to take medicine every day.

The device may be particularly helpful for people in sub-Saharan Africa, where the highest HIV and AIDS burden exists, Emilio Emini, director of the Gates Foundation’s HIV programs, said in a statement to The Huffington Post:

HIV continues to represent a substantial infectious disease burden, with some of the highest rates of infection among young people living in sub-Saharan Africa. Currently there is no effective HIV vaccine and anti-retroviral drugs that protect against HIV infection are only available in the form of a daily pill. Intarcia’s implantable Medici Drug Delivery System, which could be used to deliver long-acting anti-retroviral drugs, has the potential to solve current adherence challenges and help more people protect themselves from HIV infection.

HIV prevention medicine, which usually takes the form of a single daily pill, has revolutionized the way the world controls the spread of the incurable and potentially deadly virus. However, research shows that its effectiveness among different high-risk groups is mixed ― not for any biological reasons but because of social and cultural factors that get in the way of people and their medicine.

For instance, daily PrEP pills have an almost 100 percent effectiveness rate among gay men in California, while trials testing PrEP’s effectiveness among women in Africa showed it doesn’t significantly reduce HIV infections.

Experts hypothesize that women in poor countries may have trouble preventing HIV in general because of their status in a male-dominated society. Adhering to a daily pill regimen, or even insisting on condom use, over the objections of a partner can be difficult barriers for these women. Discreet devices like a subdermal implant, or a vaginal ring, which the National Institutes of Health tested in 2016, could help eliminate roadblocks for women who need protection from HIV but cannot store conspicuous pills in their homes or be seen at clinics picking up medicine. However, an implant that goes under the skin of the abdomen wouldn’t be noticeable to a sexual partner, wouldn’t require interruption of sexual intimacy to activate and would need to be replaced only infrequently.

Other people who might benefit from some kind of long-term HIV prevention tool include anyone for whom PrEP is recommended: those who are in a relationship with someone with HIV, those who aren’t in mutually monogamous relationships, people who use injectable drugs or people who have unprotected sex with partners of unknown HIV status.

The advantages of a long-acting implant over a daily pill have already been demonstrated when it comes to birth control. Long-acting reversible contraception, or LARC, has a failure rate of less than 1 percent, compared with 9 percent for typical birth control pill use among the general population. This is because LARCs, which last for years, don’t require women to remember to take a pill every day or get a refill every month or so.

Intarcia’s device isn’t the only implant in development. Scientists from the University of California, San Francisco are trying to develop a biodegradable implant that releases PrEP and needs replacement every 90 days, while the nonprofit Oak Crest Institute of Science is working on an implant that also shows promise. But Intarcia has an advantage over these other models because its device has already gone through advanced clinical testing for the delivery of diabetes medicine, notes Dr. Jonathan Li, an assistant professor at Harvard Medical School and Brigham and Women’s Hospital. (Li is not involved in the development of the implant.) If Intarcia’s implant is shown to work for PrEP, its device could be the earliest to hit the market.

Dr. Paul Volberding, director of the University of California, San Francisco AIDS Research Institute, also pointed out that implants have an advantage over long-acting preventive injections, another discreet, long-term solution that is being tested, as implants can simply be removed if a person develops an allergy or side effect, whereas an injection can’t be reversed.

No matter which device emerges first, a yearly subdermal implant could go a long way to help people stick with HIV prevention regimens, Li concluded.

“Taking medications every day can be a challenge, especially if that medication is being used only as a preventative measure and taken by young, healthy adults. An implantable device that only needs to be refilled once or twice a year could revolutionize HIV PrEP treatment the same way that long-acting and implantable birth control devices have broadened choices for contraception.”