Project Summary Nigeria has the 4th highest global burden of HIV and an uncontrolled epidemic. Among youth aged 15-24, HIV incidence remains high and rates of viral suppression low. The HIV epidemic in Nigeria's youth is highest in men who have sex with men (MSM) and transgender women (TW). Although external (i.e., non-governmental) funders support key population-focused centers to increase access to HIV services for MSM and TW, their reach is limited by dwindling and unsustainable funding. Efforts to improve the capacity of government clinics to reach and care for young MSM (YMSM) and young TW (YTW) as well as to implement effective, scalable, youth-specific interventions with enhanced prevention, improved case-finding, and increased ART access and adherence support for youth living with HIV (YLH) are critical to turn around lagging indicators across the HIV prevention and care continuum. However, to-date, no interventions have undergone rigorous effectiveness and implementation research in Nigeria's complex sociocultural milieu. iCARE Nigeria is a successful NICHD- funded PATC3H research partnership investigating two youth-specific interventions to improve: (1) HIV case- finding and linkage-to-care among YMSM and YTW, and (2) adherence and viral suppression among largely vertically-infected YLH on ART. Each intervention combines evidence-based peer navigation and mHealth strategies adapted to the local context; feasibility and efficacy were shown in a pilot study (UG3). We herein propose iCARE Plus, to scale out and test effectiveness and implementation outcomes on enhanced versions of the iCARE interventions within the newly formed PATC3H-IN. The iCARE Plus Clinical Research Center (CRC) will conduct hybrid effectiveness-implementation trials that will utilize an EPIS (Exploration, Preparation, Implementation, and Sustainment) framework to contextualize intervention implementation in youth aged 15-24 through new Clinical Research Performance Sites (CRPSs) in HIV “hotspots” across Nigeria's six geopolitically distinct zones. Our specific aims are: Aim 1 (Preparation): Implementation preparation will be carried out at selected government clinics in the HIV hotspots, while increasing their capacity and capability to provide services to YMSM and YTW. Aim 2 (Implementation): Test the effectiveness and implementation outcomes of enhanced versions of the iCARE interventions on: 1) HIV case-finding, linkage-to-care and PrEP uptake among YMSM and YTW and 2) viral load suppression in previously unstudied YLH newly-diagnosed and initiating ART. Aim 3 (Sustainment): Promote sustainment of the iCARE initiative and the implementation science capacity development goals of PATC3H-IN by developing a sustainability plan, including economic considerations that leverage ongoing formative research funded by an NICHD supplement, in collaboration with youth, clinic administrators and health ministries and develop IS capacity, building on our Adolescent HIV Preventio...