Abstract for: Using System Dynamics to Optimize Human Papillomavirus Vaccination Strategies in Resource-Limited Settings: A Case of Tanzania

Tanzania has a high cervical cancer burden, with 10,241 cases and 6,525 deaths annually, mainly from HPV types 16 and 18. Aligning with WHO’s 90-70-90 strategy, vaccination and screening rates do not consistently reach desired levels (>=90% vaccination coverage, >=70% screening rate) due to awareness, stigma, infrastructural, and operational challenges. Existing models lack a focus on HPV or system dynamics (SD). This study uses SD to analyze HPV vaccination strategies amid Tanzania’s transition from Gavi support. Building on our previous work with CLDs, this study combined ATM’s system design and Sterman's 5-step approaches to develop a SD model of HPV vaccination strategies. The model integrates population, vaccine supply and service provision dynamics into school-based, out of school (OOS) vaccination strategies. It is calibrated with data from two districts of Tanzania since HPV vaccination started (2018) to 2025, and validated via stakeholder discussions. Scenarios with different strategies were analyzed against their impact on vaccination coverage. Vaccination coverage reaches desired levels with regular and annual catch-ups. Vaccination coverage among OOS girls has a minimal overall contribution when school enrolment rates are high (>90%). Nevertheless, it can be improved with regular school-like schedules. Vaccination coverage increases with improved operational factors such as workforce availability, motivation, skill level and supervision coverage. The model projects increased domestic expenditure on HPV vaccination following population growth and transitioning from Gavi funding, as full self-reliance status is expected by 2042. To achieve and maintain desired HPV vaccination coverage, regular and annual catch-ups must be supplemented to primary vaccination schedules. To achieve vaccination equity, OOS vaccination should be strengthened with scheduled visits coordinated by community health workers. Strengthening vaccine operations is key to achieving and sustaining desired vaccination coverage. The country should raise domestic financial capacity to sustain HPV vaccination services in the wake of Gavi transitioning.