HIV incidence in people receiving government-subsidised pre-exposure prophylaxis in Australia: a whole-of-population retrospective cohort study.

Background: HIV pre-exposure prophylaxis (PrEP) is highly effective and has been government subsidised in Australia since April, 2018. We examined HIV incidence over 5 years in a retrospective observational cohort of people who had received subsidised PrEP.

Methods: Linked de-identified dispensing records for all government-subsidised oral PrEP, HIV antiretroviral therapy (ART), and hepatitis C treatment were used. We included all people dispensed subsidised PrEP from April 1, 2018, to March 31, 2023, and examined records up to Sept 30, 2023. Exposure was measured from date of first PrEP prescription and days covered by PrEP calculated for individuals based on quantity and date supplied. Assuming that HIV was diagnosed 30 days before ART initiation, we imputed the date of acquisition as the midpoint between the diagnosis and the later of the last PrEP prescription or 6 months before the diagnosis. We calculated HIV incidence and its predictors using Poisson regression.

Findings: We included 66 206 people dispensed PrEP: 64 757 (97·8%) were men; median age was 33 years (IQR 27-43). 207 people acquired HIV, with an overall incidence of 1·07 per 1000 person-years (95% CI 0·93-1·23). Incidence was 2·61 per 1000 person-years among those dispensed PrEP once only. Using this group as a comparator, those with 60% or more days covered by PrEP had a 78·5% reduction in incidence (0·56 per 1000 person-years, p<0·0001) and those with less than 60% days covered had a 61·6% reduction (0·99 per 1000 person-years, p=0·0045). Independent predictors of HIV acquisition were a record of hepatitis C treatment (9·83 per 1000 person-years, adjusted incident rate ratio [aIRR] 8·70, 95% CI 4·86-15·56), only attending prescribers outside of areas with a high estimated prevalence of gay men (1·66 per 1000 person-years, aIRR 1·50, 1·08-2·09), age 18-29 years (1·33 per 1000 person-years, aIRR 1·56, 1·11-2·21), and earlier year of first PrEP.

Interpretation: The low observed incidence of HIV among people receiving government-subsidised PrEP highlights the success of a national programme of oral PrEP scale-up in achieving sustained reduction in community HIV transmission. However, incidence varied greatly, indicating that more research is needed to understand why people were not taking PrEP at times of risk and emphasising the need for new interventions focused on this population to achieve elimination of HIV transmission. Individuals dispensed PrEP once only and less frequent users might benefit from more support.

Funding: None.