Like other PrEP drugs, if enough of the medication is present when a person is exposed to HIV, it can prevent the virus from taking hold and causing a lifelong infection. Because lenacapavir is long-acting, it requires only two injections per year.

Clinical trials have shown that six-monthly injections of lenacapavir are almost 100 percent protective against becoming infected with HIV. But big questions remain over the drug’s affordability.