High Levels of Prevention-effective Adherence to HIV PrEP

An Analysis of Substudy Data From the EPIC-NSW Trial

Benjamin R. Bavinton, PhD; Stefanie Vaccher, PhD; Fengyi Jin, PhD; Garrett P. Prestage, PhD; Martin Holt, PhD; Iryna B. Zablotska-Manos, PhD; Rebecca Guy, PhD; Janaki Amin, PhD; David J. Templeton, PhD; Barbara Yeung, MPH; Mohamed A. Hammoud, PhD; David Lewis, PhD; David Baker, MBBS; Nila Dharan, MD; Anna M. McNulty, MBBS; Andrew E. Grulich, PhD


J Acquir Immune Defic Syndr. 2021;87(4):1040-1047. 

In This Article


In the context of a large-scale PrEP implementation trial, prevention-effective adherence to PrEP during observed weeks was close to 100% among participants of a large substudy and most substudy participants sustained high levels of protection from PrEP by aligning PrEP use with periods of sexual activity and risk. Although it must be acknowledged that those who volunteered to participate in the substudy may have had different patterns of adherence to those who did not, our findings nonetheless illustrate the additional benefits of measuring pill taking during the period in which sexual events occur. This approach can help explain high levels of PrEP effectiveness even when PrEP discontinuation or periods of suboptimal adherence seem relatively common given that measurement of pill taking without reference to sexual behavior may be likely to overestimate HIV risk.