HIV seroconversions on PrEP in Australian study are linked to low adherence

1 September 2022. Related: HIV prevention and transmission.

Kirk Taylor, HIV i-Base

A large Australian PrEP implementation study involving 9,596 participants over two years only reported 30 people becoming HIV positive (0.31%) and these cases were linked to low adherence. Only one seroconversion was attributed to ART resistance (FTC: M184V mutation).   

Seroconversions were all men that identified as gay/bisexual (97%) and reported condomless sex in the previous three months (90%). Median age was 31 years (IQR: 25 to 38). Median time from starting PrEP to diagnosis was 409 days (IQR: 347 to 656) and median viral load was 61,000 copies/mL. Two-thirds of participants were diagnosed with an additional STI, similar to rates for the overall group. 

Adherence was tracked through dispensing logs, with perfect adherence defined as taking five or more doses/week with <4 doses/week considered insufficient.

Reasons for low adherence included recent change in sexual activity/entering monogamous relationships (n=5), renal impairment (n=1), affordability of PrEP (n=1) and not packing PrEP for vacation (n=1).

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These results show that oral PrEP continues to be highly effective when taken as prescribed but that the difficulties of adherence still leads to HIV seroconversions.

It is notable that this large cohort only identified low adherence as a factor involved in the new cases.

Recent experience at the London clinic at 56 Dean Street, where more than 25,000 people have been prescribed oral PrEP, included 7 out of 52 seroconversions (13%) which occurred despite good adherence. Only one of these was linked to drug resistance. [2]

References

1. Dharan NJ et al. Characteristics of HIV seroconversions in a large prospective implementation cohort study of oral HIV pre-exposure prophylaxis in men who have sex with men (EPIC-NSW). Clinical Infectious Diseases, ciac660. (19 August 2022).
   https://doi.org/10.1093/cid/ciac660
2. 56 Dean Street reports M184V common with recent low adherence to PrEP and seven transmissions with good adherence. HTB (20 December
   2021).
   https://i-base.info/htb/41912