PROJECT SUMMARY Understanding the factors related to for whom and why evidence-based human papillomavirus (HPV) vaccine implementation strategies are effective and sustainable will inform the development of tailored or complementary strategies aimed to increase health equity. Rates of HPV vaccination among adolescents in the United States continue to remain below recommendations. Florida adolescents are particularly vulnerable due to the state’s rank of 4th for HPV-related cancer diagnoses, but 46th for HPV vaccine initiation (≥1 dose) and 47th for up-to-date rates (2 doses when first dose < 15 years; 3 doses when first dose ≥ 15 years). Despite evidence of HPV vaccination disparities by geography and social determinants of health (SDOH), most HPV vaccination implementation strategies have employed universal methods or tailored education material by vaccine concerns and ignored the potential influence of key SDOH-related differences. Text & Talk is a 30- clinic pragmatic trial in Florida assessing the effectiveness of two HPV vaccine implementation strategies: (a) provider-targeted recommendation training encouraging providers to use a C-LEAR – Counsel, Listen, Empathize, Answer, and Recommend – approach and (b) parent-targeted text messages. Text & Talk has 58 participating providers (37 trained during the study period and 21 to be trained after data collection) and 7,837 11- to 12-year-olds randomized for their parents to receive text messages about the HPV vaccine. The goal of this proposal is to understand the factors related to for whom and why the Text & Talk implementation strategies were effective and sustainable. For the provider-targeted training, the hypothesis is that providers will have different experiences with implementing and sustaining C-LEAR in their practice that will guide improvement and refinement of future trainings. For the parent-targeted text messages, text message effectiveness is hypothesized to be differentially moderated by parental and neighborhood SDOH. Specific aims are to: (1) Evaluate providers’ experiences with and sustainability of integrating C-LEAR into their practice; and (2) Measure moderation of the effectiveness of a parent-targeted text message intervention on increasing HPV vaccination by social vulnerability themes. Hypotheses will be evaluated by triangulating data collected in Text & Talk with additional data collected during the extension period via mixed methods including in-depth, semi-structured provider interviews, provider behavioral surveys about intent to sustain and continue the use of C-LEAR, and spatially linking adolescent addresses to SDOH measures at census block group. The innovations are a more in-depth focus on provider learning than previous studies and expanding existing understanding of HPV vaccine reminder/recall moderation from primarily demographic variables to parent factors and well-established, multicomponent risk scores measuring neighborhood-level SDOH. The significance ...