Nondaily pre-exposure prophylaxis, or PrEP, demonstrated decreased efficacy compared with daily PrEP, especially among men who have sex with men in the United States, according to a study published in Clinical Infectious Diseases.
“HPTN 067/ADAPT was designed to assess whether nondaily use of PrEP, compared with daily use, would provide equivalent PrEP coverage of sex acts and decrease self-reported drug side effects over 24 weeks, while requiring a smaller number of pills,” Dobromir Dimitrov, PhD, senior staff scientist in the division of vaccine and infectious disease division at the Fred Hutchinson Cancer Research Center, and colleagues wrote. “Mathematical models are often used to assess the impact of HIV prevention and inform public health policies. The goal of our modelling study was to predict the effectiveness of different PrEP regimens in reducing HIV incidence among [men who have sex with men (MSM)], based on data collected at the HPTN 067/ADAPT sites in Harlem and Bangkok.”
The researchers adjusted an individual-based mathematical model that had been published previously to predict the efficacy and effectiveness of different dosing regimens by comparing HIV incidence with and without PrEP use.
Researchers anticipated that PrEP would be highly protective, with 85% to 96% efficacy across regimens and sites, for fully covered acts. The findings demonstrated that PrEP was more protective for partially covered acts in Bangkok (71%-88% efficacy) than in Harlem (62%-81% efficacy). The researchers’ model estimated 80%, 62% and 68% effectiveness of daily, time-driven and event-driven PrEP for MSM in Harlem compared with 90%, 85% and 79% for MSM in Bangkok.
Overall, PrEP was more effective among MSM in Thailand than in the U.S. due to more fully covered sex acts and more pills taken around partially covered acts. Nondaily PrEP was less effective than daily PrEP, particularly in the U.S. where coverage of the sex act correlated with substantially higher daily use.
The results provide “useful projections” about the effectiveness of daily and nondaily use of PrEP when it is being considered for large-scale implementation among MSM in different regions that follow WHO recommendations, according to Dimitrov and colleagues.
““Our analysis suggests that a one-size-fits-all policy may not be appropriate when PrEP implementation programs are designed,” the authors concluded. “We also reiterate that the success of PrEP interventions will heavily rely on optimal adherence, which can be particularly challenging for long-term use of daily PrEP by healthy individuals. Nondaily PrEP regimens carry the potential to reduce the pill burden [for] some people at risk, but the effectiveness of these regimens should be further investigated to inform the design of optimal personalized PrEP recommendations in the future.” – by Caitlyn Stulpin
Disclosures: Dimitrov reports receiving a grant from the Bill and Melinda Gates foundation outside of the submitted work. Please see the study for all other authors’ relevant financial disclosures.