  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
or 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.
