Vaccine Supply Chains in Resource-Limited Settings: Mitigating Rainy Season Disruptions

Immunization is widely recognized as one of the most successful and cost-effective health interventions, preventing two to three million deaths from vaccine-preventable diseases each year. Although progress has been made in recent years, substantial operational challenges persist in resource-limited settings with frequent stock-outs contributing to sub-optimal immunization coverage and inequality in vaccine access. In this paper, we investigate the role of rainy season induced supply chain disruptions on vaccination coverage and inequalities. We develop a modeling framework combining spatial modeling--to predict flood disruptions in road networks--and a discrete-event simulation of a multi-tiered vaccine supply chain (VSC). Our models are fitted and validated using data from the Malagasy VSC network. Our baseline simulation predicts the national vaccination coverage with good accuracy and suggests that 67% of regions with low reported immunization coverage are affected by rainy season disruptions or operational inefficiencies, causing significant geographical inequalities in vaccine access. We investigate various mitigation strategies to increase the resiliency of VSCs and find that by strategically placing buffer inventory at targeted facilities prior to the rainy season the proportion of children receiving all basic vaccines in these areas is increased by 7% and the geographical inequality in vaccination coverage is reduced by 11%. By also increasing the replenishment frequency from every third month to every month, the national vaccination coverage improves by 37%. Our results contribute to achieving the UN Sustainable Development Goals (SDGs) by providing actionable insights for improving vaccination coverage (SDG 3) and investigating the resiliency of the VSC to increased flooding due to climate change (SDG 13).