A Complex Systems Approach to Modelling Childhood Immunisation Coverage Dynamics in Northern Nigeria

Childhood immunisation coverage in northern Nigeria exhibits non-linear dynamic patterns that are inadequately explained by linear epidemiological models, reflecting the complex adaptive interactions between community, health system, and political determinants that characterise this low-coverage context. This study applied a complex systems approach to modelling immunisation coverage dynamics in North West and North East Nigeria. A multi-method complexity research design was employed, combining system dynamics modelling with causal loop diagram construction, agent-based simulation, and longitudinal case analysis. System dynamics modelling drew on a comprehensive causal loop mapping exercise involving 38 stakeholder workshops with immunisation programme managers, community mobilisers, healthcare workers, religious leaders, and parents across 12 LGAs in Kano, Sokoto, and Borno States. Causal loop diagrams identified 47 feedback relationships organised into 12 reinforcing and 8 balancing feedback loops. System archetypes identified included shifting the burden dynamics (where campaign-based coverage gains reduce investment in routine system strengthening), eroding goals dynamics (where temporary coverage dips lead to reduced performance targets), and success to the successful dynamics (where high-performing communities continue to receive programme resources). Agent-based simulation modelling in NetLogo explored how individual caregiver decision dynamics aggregate to produce population-level coverage patterns. Scenario analyses identified three high-leverage interventions: demand-side social mobilisation, vaccine hesitancy peer network disruption, and supply chain inventory buffer investment. The study constitutes an original methodological contribution to immunisation systems science and provides a complexity-informed framework for northern Nigerian immunisation programme strategy.

Keywords: complex systems, immunisation coverage, northern Nigeria, system dynamics, agent-based modelling