Introduction: HIV incidence among men who have sex with men (MSM) in Nigeria was 5.8-23.1/100 person years (PY) in 2019, exceeding the ≥ 3/100 PY recommended by the WHO for initiation of HIV pre exposure prophylaxis (PrEP).

Objectives: To estimate the correlation between self-reported PrEP adherence (SRPA) and PrEP biomarkers (assay), to assess the association between perceived social support (SS) with protective PrEP adherence (PA), and to estimate the effect of PrEP use on behavioral outcomes.

Methods: In this open-label, one-year follow-up, prospective cohort study, MSM living in Abuja were introduced to PrEP in clinic or community based setting for five scheduled visits (baseline, months 1, 3, 6, and 9). Clinical information and sexually transmitted infection (STI) samples were collected at each study visit. PrEP biomarker assays were conducted at month 3 and 9. The correlation between SRPA and assay results was estimated with Spearman’s correlation. Logistic regression estimated adjusted odds ratio (aOR) between SS (informational, instrumental and informational) and PA. A conditional logistic regression estimated aOR of STIs (Rectal and urethral Gonorrhea [NG] and Chlamydia) of behavioral outcomes (Condomless anal intercourse [CAI] and concurrent sex partnerships) comparing pre-PrEP versus Post-PrEP period.

Results: Of 400 that initiated PrEP between April 2018 and May 2019, 219 had ≥1 assay, with median age 23 (interquartile range 20-27) years. Of this 219, sixty-six (30%, 95% CI: [0.24, 0.36]) had ≥1 PA. A total of 206 were eligible for pre-post-PrEP period analysis. In multivariable analysis, participants with perceived emotional SS had 42% increased odds (aOR: 1.42, 95% CI: [1.00, 2.00]) of PA. In the post-PrEP period, compared with pre-PrEP period, participants had 3.5 times increased odds (OR: 3.53, 95% CI: 1.10, 11.35) and 51% decreased odds (aOR: 0.49, 95% CI: 0.28, 0.84) of rectal NG diagnosis and reporting CAI, respectively, but no significant changes in prevalence of all STIs.

Conclusion: There was no association between SRPA and assay; perceived emotional SS was a facilitator of PA. We demonstrated trends of PrEP associated sexual behavioral modifications but further studies are required. Our study findings have implications for PrEP implementation in Nigeria and similar settings.