Project Summary/Abstract Overview and Background. This is a proposal for a hybrid 2 implementation-effectiveness randomized controlled trial (RCT) of FINISHING HIV, an implementation strategy bundle of a social network support component and a one-stop-shop PrEP component to improve PrEP initiation of Latino men who have sex with men (LMSM). PrEP can reduce HIV transmission by up to 99%,1 however, PrEP services are not being sufficiently accessed by Latinos in Miami, the epicenter of the HIV epidemic in the US.2 Further, LMSM who do not self-identify as gay have lower PrEP awareness than LMSM who self-identify as gay.3 To prepare for this study, we have developed an innovative approach that tailors LMSM engagement based on sexual self-identity using community-based social events and pharmacies. Preliminary work. The trial is a direct next step from our “Ending the HIV Epidemic” (EHE) planning supplements, where we conducted the needed preliminary study to launch this hybrid trial, and with ISCI3 support, the team jointly assessed feasibility, refined strategies and built a logic model informed by local context needs and preferences. Over the past two years, the PI has built partnerships with Latinos Salud (a local HIV agency for LMSM) and CVS Health. Design. We will use an innovative network-based approach informed by the PI’s K99/R00 funded research and Social Contagion Theory,4 which states that health behavior preferences, including PrEP initiation, are affected by opinions and attitudes prevailing in one’s social environment, and spread through friendship networks.5 Penetration at pharmacies and social events will lead to random assignment of the participants to either FINISHING HIV (social network support component + one-stop-shop PrEP component; N=24 seeds and 288 LMSM friends) or to standard health promotion (N=312). Participants will be assessed at baseline, and receive follow ups and dried blood spots collection at 6 and 12 months to quantify tenofovir diphosphate concentrations. For implementation (Aim 1), we will use RE-AIM framework6 to evaluate Reach (the extent to which high risk persons initiate participation in the program), and Implementation (the extent to which implementation strategies are delivered as designed) of FINISHING HIV. We will also use Consolidated Framework for Implementation Science Research7 to examine contextual factors associated with Reach and Implementation (e.g., facilitators and challenges or barriers to reach and implementation; participants reaction to these strategies). We will compare effectiveness (Aim 2) of the strategies in PrEP initiation (primary outcome), as well as PrEP knowledge, retention, and adherence (secondary outcomes). We will identify theory-based moderators (e.g., recruitment at social events vs. pharmacies) and social network mediators of intervention effects. We will also assess how friendship network structural evolutions contribute to increasing PrEP initiation. Implications. Our use...