Recent data indicate that PrEP has overtaken condoms as the most common HIV prevention strategy among Australian gay and bisexual men.

With its 99% efficacy rate among these men, PrEP has been a game changer in HIV elimination.

Scientists, however, have struggled to explain why PrEP use by women — who account for more than half of adults living with HIV globally — fails to afford them a similar level of protection.

Several international trials have reported widely divergent efficacy rates ranging from -49% to 75% for daily oral PrEP, and from 0% to 39% for topical formulations.