A study found that two injections a year of a drug currently used to treat HIV was highly effective in preventing infection in young women and teens in Africa.

A drug called lenacapavir has demonstrated 100% efficacy in preventing HIV infection during a Phase 3 trial, according to data released by drugmaker Gilead and published in the New England Journal of Medicine.

Traditionally, prevention of HIV, or human immunodeficiency virus, has relied on daily medications like Truvada or, more recently, bimonthly injections of Apresput.

The introduction of lenacapavir doses, given twice a year, may provide a new, highly effective prevention method.

In a trial of more than 5,000 HIV-negative women and adolescents in Africa, none of the women who received lenacapavir injections twice a year developed HIV.

These findings were also presented at the International AIDS Conference in Munich.

“These impressive results suggest that if approved, lenacapavir could be a highly effective, tolerable, and discreet option for twice-yearly PrEP that could potentially improve PrEP uptake and persistence, helping us reduce HIV among cisgender women globally,” Linda-Gail Bekker, director of the University of Cape Town’s Desmond Tutu HIV Centre, said in a statement.

The study, known as the PURPOSE 1 trial, included adolescent girls and young women in South Africa and Uganda who were randomly assigned to receive either lenacapavir injections every 26 weeks or daily HIV medications.

The study was double-blind, so participants didn’t know which treatment they were receiving.

About 69% of people taking lenacapavir experienced injection site reactions, compared with 35% in the placebo group. However, no significant safety concerns were reported.

At 26 weeks, 55 HIV infections were observed: zero in the lenacapavir group, 39 in the daily emtricitabine-tenofovir alafenamide group, and 16 in the daily emtricitabine-tenofovir disoproxil fumarate group.

Although lenacapavir is not yet approved for HIV prevention anywhere in the world, it is approved by the US Food and Drug Administration (FDA) to treat HIV in adults in combination with other antiretroviral medications.

The estimated cost of the drug is more than $40,000 per year according to the manufacturer’s list price, or about $39,000 per year according to the average wholesale price.

As lenacapavir continues to be studied for HIV prevention, questions remain about its cost and availability.