Background
Daily and on-demand oral pre-exposure prophylaxis (PrEP) have been shown to be effective at preventing HIV acquisition among cisgender men and transgender women, but only daily PrEP is recommended for cisgender women. On-demand PrEP may be a valuable option to improve PrEP uptake, effective use, and persistence in cisgender women. We use data from HPTN 067 study to estimate effectiveness achieved by different non-daily PrEP options and investigate which sub-groups of women may benefit most from using them.
Methods
We created a synthetic cohort of PrEP users using data on the frequency of sex acts, condom use, and PrEP pill taking from the Cape Town site of the HPTN 067 study. We simulated PrEP use and HIV incidence with hypothetical use of the three PrEP regimens tested in HPTN 067: daily, time-based (2 pills/week +1 pill after sex), and event-based (1 pill before +1 pill after sex) PrEP, as well as 2-1-1 (2 pills before +1 pill each of the following two days after sex) PrEP for six months each. We estimated PrEP effectiveness based on the number of pills taken around sex acts. Adherence to 2-1-1 PrEP, which was not tested in the HPTN 067, was informed by observed adherence to event-based PrEP. Assignment to 2-1-1 PrEP based on daily PrEP adherence, sex act frequency, and hypothetical “optimal” criteria combining better effectiveness and/or lower pill burden were also analyzed.
Results
We estimated effectiveness of 81% for daily, 46% for time-based, 42% for event-based, and 59% for 2-1-1 PrEP for HPTN 067 participants in Cape Town (see Figure). PrEP users with low adherence to daily PrEP (less than 2.8 pills per week) benefited most from non-daily PrEP. In this subgroup, comprising 8% of the cohort, PrEP effectiveness increased from 39% to 43% when switching from daily to 2-1-1 PrEP while pill taking decreased from 2 to 1.5 pills per week. We found no advantage in assigning 2-1-1 PrEP by sex act frequency. The effectiveness of hypothetical “optimal” assignment was comparable to assignment based on low PrEP adherence.
Conclusions
On-demand PrEP could benefit women with low daily PrEP adherence by decreasing the number of days on which pills need to be taken and increasing effectiveness compared to a daily regimen. This would be a valuable and easy-to-implement additional option in places where daily oral PrEP is already available.