Abstract
We assessed the association between PrEP adherence support interventions and intracellular tenofovir-diphosphate (TFV-DP) levels, a biomarker for PrEP adherence, using data from 368 South African and Zimbabwean adolescent girls and young women enrolled in the HIV Prevention Trials Network 082 trial from 2016 to 2018. Group-based trajectory modeling identified trajectories of TFV-DP levels and adherence support interventions, including weekly two-way SMS and optional monthly adherence clubs. Two trajectories of TFV-DP levels were identified: a consistently low trajectory (N = 248, 67.4%, with consistent TFV-DP levels of 100 fmol/punch) and a high-decreasing trajectory (N = 120, 32.6%, with TFV-DP levels decreasing from approximately 900 to 500 fmol/punch). Two trajectories were also observed for adherence club attendance: consistently moderate (N = 249, 67.7%, attended approximately two out of three clubs in a three-month period) and low-increasing (N = 119, 32.3%). Similarly, SMS response patterns included a consistently high engagement group (N = 222, 66.1%), who responded to approximately 90% of messages, and a consistently low engagement group (N = 114, 33.9%). Women with consistently high SMS responses had higher odds of being in the high-decreasing TFV-DP levels trajectory group (Adjusted Odds Ratio [AOR]: 6.6; 95% CI 2.8-15.5; p < 0.001), while those with a consistently moderate adherence club attendance trajectory had an AOR of 1.3 (95% CI 0.5-3.3, p = 0.620) for being in the same group. Use of PrEP was aligned with the higher response trajectories of SMS responses but not with attendance to adherence support clubs.