Bouwen aan een veerkrachtig en duurzaam immunisatiesysteem in Tanzania

Over the past decades, immunization initiatives such as the Global Vaccine Action Plan (GVAP) and the African Regional Strategic Plan for Immunization have improved access to vaccines and inspired in immunization coverage across the world. This progress has been reflected in Tanzania with the reductions in the incidence of vaccine-preventable diseases (VPDs) and under-five mortality rate since 1990. The COVID-19 pandemic affected this progress by disrupting essential health services, including routine immunization activities. As a results, cases of VPDs re-emerged, risking the lives of many children. To sustain the benefits of immunization, it is critical to build more resilient and sustainable immunization systems (IMS), a call made by the Immunization Agenda 2030, and several other global, regional and local initiatives. The Tanzanian National Immunization Strategy (NIS) 2021-2025 identifies several strengths, weaknesses, opportunities and threats (SWOTs) across various thematic areas. This span service delivery; program management and financing; human resource management; vaccine supply, quality and logistics; data management; demand generation and communication; as well surveillance of VPDs. These areas represent complex structural elements that govern the IMS. To understand their intrinsic interactions and how they impact immunization performance, as well as formulating strategies that cut across these interactions, a holistic approach is required. Systems thinking can provide such a holistic insight into complex systems, but there is limited evidence of its application for the IMS in Tanzania. This study aimed to contribute to building immunization system resilience and sustainability by employing stakeholder-based approaches to develop qualitative and quantitative model-based decision support tools. These approaches included in-depth interviews, focused group discussions and group model building workshops (GMB). These were supplemented with literature reviews and cross-sectional quantitative studies to develop causal loop diagrams (CLDs) and a system dynamics (SD) model. Chapter 1 provides an overview of global, regional and national immunization initiatives, including NIS, and discusses the utility of systems thinking and modelling approaches in IMS. Chapter 2 highlights challenges impeding vaccine access and uptake, across sub-Saharan Africa (SSA) and discusses mitigation strategies employed. This chapter identifies concerns on the sustainability and resilience of African IMS. While improvement strategies have been employed, very few were human-centered design approaches for decision support. Chapter 3 presents a CLD of mechanisms impacting vaccine uptake and coverage and discusses pathways towards sustainability and resilience. The CLD links demand and supply dynamics and highlights potential leverage points for sustainable and resilient immunization services, including vaccine acceptability and operational challenges. Chapter 3 sheds light on the significance of adequate investment and accountability to address these leverage points. It outlines critical areas of investment, including vaccine safety surveillance and communication, awareness campaigns, vaccination sites, workforce capacity and vaccine operations. Chapter 4 presents a SD model developed following lessons learned from previous chapters. This model uses Human Papillomavirus (HPV) Vaccination data from two districts in Dar es Salaam and Manyara regions in Tanzania as case study. This chapter presents the analysis of different scenarios related to HPV vaccination strategies implemented in Tanzania since the vaccine was introduced in 2018 until 2025. It further discusses on financial sustainability based on projections of population growth and transitioning from Gavi (the Global Vaccine Alliance) financial support. The analysis shows that regular catch-ups and annual campaigns must be added and enforced into primary vaccinations both in school and out of school to achieve the desired HPV vaccination coverage rates and vaccination equity. The model further highlights that vaccination coverage improves with increasing operational factors such as workforce availability, motivation and skills, as well as supervision coverage. Chapter 5 presents the overall conclusions of the thesis and gives recommendations for the sustainability and resilience of IMS. These are followed by discussions on future research directions and finalized with personal lessons learned from the PhD trajectory.