This project evaluates the implementation strategy of the delivery of lenacapavir pre-exposure prophylaxis (LEN PrEP) - a newly available long-acting, injectable medication for human immunodeficiency virus (HIV) prevention - via a mobile health van model for people who are unstably housed in Los Angeles County (LAC). People who are unhoused or are facing housing instability experience significant barriers to accessing HIV prevention care in traditional clinic settings. In 2022, approximately 13% of newly diagnosed HIV cases in LAC were experiencing homelessness, a 36% increase over the prior period. The study will work with the University of California, Los Angeles (UCLA) Health's Homeless Healthcare Collaborative (HHC), which operates mobile health vans staffed by clinicians, social workers, and community health workers, to bring LEN PrEP directly to community settings, such as shelters, encampments, community centers, and transitional housing facilities.

This study has three primary aims:

1. Characterize uptake of LEN PrEP among unstably housed people in LAC receiving health services via HHC's mobile program.
2. Evaluate how many study participants stay on LEN PrEP through 52 weeks.
3. Understand costs, acceptability, and sustainability of the mobile LEN PrEP delivery model.

Access to HIV prevention services for unstably housed people in LAC has been limited due to barriers in seeking care at health facilities. Unstably housed people face barriers including competing life priorities (such as seeking food, shelter, and employment), low health literacy, particularly around HIV prevention, and comorbidities such as substance use and mental health disorders. A mobile healthcare service that offers LEN PrEP is ideal to help overcome these barriers by providing a low-complexity biomedical PrEP option in locations where unstably housed people congregate (i.e., shelters, encampments, community centers, and transitional housing facilities). The UCLA Health HHC was founded in January 2022 and currently operates six mobile vans, which deliver urgent care, primary care, behavioral health services, and medication-assisted treatment for substance use disorders. At least one mobile van is in the field offering services every day of the week, including weekends. The van is staffed by clinicians and community health workers, who link clients to social services. HHC recently began providing point-of-care HIV and sexually transmitted infection (STI) testing and is well-positioned to integrate LEN PrEP into their program.

Based on Andersen's behavioral model (3) and using Proctor et al's implementation outcomes (4), the investigators propose the following:

Aim 1. Characterize uptake of LEN PrEP among unstably housed people in LAC receiving health services via HHC's mobile program. People without HIV receiving health services via the HHC mobile unit (n=100) will be offered LEN PrEP. A baseline survey will be performed (sociodemographics, clinical information, HIV risk, PrEP knowledge, self-efficacy for health care, and acceptability of mobile PrEP offer). The primary outcome will be uptake, defined as receiving a first injection of LEN PrEP and both oral doses on days 1 and 2. All participants will have the option to receive an Apple AirTag to enable directly observed therapy (DOT) for the second oral LEN dose and for follow-up LEN PrEP injections.

Aim 2. Evaluate LEN PrEP persistence through 52 weeks. Participants who initiate LEN PrEP will receive ongoing visits from the HHC mobile unit for HIV/STI testing every 3 months and HIV testing and LEN injections every 6 months. The study will estimate the share of initiators who receive LEN PrEP through week 52 ("persistence" defined as completing the third dose on-time [+/-14 days]). Surveys will be performed with all individuals who can be reached at 52 weeks (both persisters and non-persisters), to understand acceptability of mobile LEN PrEP, barriers to this care, and satisfaction with care.

Aim 3. Understand costs and sustainability of the mobile LEN PrEP delivery model. Costs will be collected from the health system perspective. The study will calculate the cost per person who initiates LEN PrEP, and cost per person persisting over 52 weeks.

The investigators will additionally perform in-depth interviews with stakeholders, including HHC leadership and van staff, public health leaders, and community leaders (n=25) to understand acceptability and feasibility of this model, and service- and system-level factors hypothesized to be associated with scalability and sustainability of the program.

Inclusion Criteria:

• Being reached for mobile health services by a UCLA HHC mobile van
• ≥18 years of age
• Able to provide informed consent
• English or Spanish-speaking
• Willing and able to comply with study procedures
• HIV unknown or negative status and HIV negative based on rapid 4th generation Ag/Ab test on the day of enrollment
• At-risk for HIV, based on clinician assessment (based on CDC guidelines; includes any individual requesting PrEP, regardless of reported risk factors for HIV)
• Pregnant and breastfeeding women/people can be offered LEN with counseling about benefits and risks.

Exclusion Criteria:

• Any clinical or psychosocial condition or prior therapy that, in the opinion of the investigator, would make the participant unsuitable for the study or unable to take LEN PrEP
• Known hypersensitivity to the study drug, the metabolites, or formulation excipient
• BMI <35 kg/m2 (77 pounds)
• On oral or other long-acting PrEP and unwilling to discontinue
• Already taking LEN for HIV prevention
• Known HIV diagnosis or positive 4th generation HIV Ab/Ag test (on day of enrollment) or subsequent lab-based confirmatory testing.

The subject population consists of adults 18 years and older being reached for care by the UCLA Health Homeless Healthcare Collaborative (HHC) and offered lenacapavir for HIV prevention.

Anonymized data can be shared after all primary and secondary study analyses have been completed and with appropriate ethical approval and agreement permissions. Study leadership will review requests for data-sharing on a case-by-case basis.

Data will be available once all primary and secondary analyses have been completed (estimated to be January 2028)

Anonymized data can be shared after all primary and secondary study analyses have been completed and with appropriate ethical approval and agreement permissions. Study leadership will review requests for data-sharing on a case-by-case basis. Data sharing format will be determined at the time of request based on type(s) of data requested.