Pediatric vaccine tender scheduling in low- and middle-income countries

Effective and efficient scheduling of vaccine distribution can significantly impact vaccine uptake, which is critical to controlling the spread of infectious diseases. Ineffective scheduling can lead to waste, delays, and low vaccine coverage, potentially weakening the efforts to protect the public. Organizations such as UNICEF (United Nations Children's Fund), PAHO (Pan American Health Organization), and GAVI (Gavi, the Vaccine Alliance) coordinate vaccine tenders to ensure that enough supply is available on the international market at the lowest possible prices. Scheduling vaccine tenders over a planning horizon in a way that is equitable, efficient, and accessible is a complex problem that involves trade-offs between multiple objectives while ensuring that vaccine availability, demand, and logistical constraints are met. The current method for scheduling tenders is generally reactive and over short planning horizons. Vaccine tenders are scheduled when supply is insufficient to cover demand. We propose an optimization model to dynamically and proactively generate vaccine tender schedules over long planning horizons. This model helps us address the following research questions: What should the optimal sequencing and scheduling of vaccine tenders be to enhance affordability and profit over long time horizons? What is the optimal tender procurement schedule for single/multiple antigen scenarios? We use several real-life data sources to validate the model and address our research questions. Results from our analysis show when to schedule vaccine tenders, what volumes manufacturers should commit to, and the optimal tender lengths to satisfy demand. We show that vaccine tenders tend towards maximum lengths, generally converge over long time horizons, and are robust to changes in varying conditions.