HIV Incidence in users of PrEP in Australia

[Jim Allen]

Aidsmap article in full: https://www.aidsmap.com/news/mar-2024/far-fewer-hiv-infections-australian-prep-users-consistent-use-key

In Brief:

While we know that PrEP is highly effective at preventing HIV transmission at the individual level, questions remain regarding its effectiveness as an intervention in the population. One challenge for researchers is choosing who to compare to people who are eligible for PrEP and use it. It is unhelpful to compare them to people who would not be eligible for PrEP, as behaviours that increase vulnerability to HIV would differ substantially.

Many country-level comparisons have looked at infections before and after the rollout of PrEP. However, there can be problems with this approach as the number of annual new HIV infections in the pre-PrEP era was most likely higher anyway, and reductions have happened over time independent of PrEP.

Medland and colleagues considered a direct comparison of people eligible for PrEP: those who continue taking it compared to those who have been prescribed it but have only filled one prescription, and not returned for subsequent refills.

Using de-identified government dispensing data, the researchers estimated the number of new HIV infections among people who regularly took PrEP between 2018 and 2023, compared to those who only filled one PrEP prescription during this period. They also considered prescriptions for ART, with the assumption that an individual who had been prescribed both PrEP and ART seroconverted during this period. Additionally, they looked at hepatitis C treatment prescriptions.

During the study period, 66,206 people were dispensed PrEP. Only a small percentage were women (2%). While 19% received PrEP once only, the majority (53%) had received PrEP more than once, yet the proportion of total days covered by PrEP for this group was less than 60%. A third group (28% of the sample) were more adherent: they received PrEP more than once and had a proportion of total days covered by PrEP of over 60%.

Of all the people who were dispensed PrEP, there were 207 new HIV infections. People who only received PrEP once comprised 30% of the infections, while the low-adherence group comprised 55% of new infections. As expected, the high adherence group comprised the least new infections at 15%. Most of those who had only received PrEP once were off it for a long time before being prescribed ART – usually over a year.

Compared to those who had only received PrEP once, incidence was 62% lower in the group that used it more than once but had less than 60% of days covered. However, for the more adherent group (with PrEP coverage over 60% of the time), this jumped to HIV incidence being 79% lower.

Medland concluded that while these data are great news for PrEP programmes – they clearly show the benefits of remaining on PrEP.

https://www.croiconference.org/abstract/hiv-incidence-in-users-of-hiv-preexposure-prophylaxis-in-australia-a-whole-of-population-analysis/