Estimating future vaccine manufacturing capacity requirements using discrete event simulation: a case study on Africa's 2040 vision

The Africa CDC's New Public Health Order aims to improve health, regional self-reliance, and health security by boosting local vaccine manufacturing capacity from <1% in 2022 to 60% by 2040. Although multiple studies have examined vaccine manufacturing capacity in Africa, none quantified future vaccine manufacturing capacity requirements and complexities in capacity planning. We fill this gap by integrating a deterministic approach and discrete event simulation (DES) to estimate vaccine manufacturing capacity requirements and assess the impact of process variability and uncertainty on manufacturing capacity needs. A total of 51 experts were interviewed to design vaccine-specific supply chain networks, collect, and validate data on process-specific parameters. Our findings reveal that deterministic approach provides optimistic capacity estimates but realistic estimates of capacity requirements is possible using DES as it captures variability and uncertainty inherent in vaccine manufacturing. Further evidence shows that reduction in batch yield at any manufacturing stage significantly reduces throughput, while the impact of high batch deviations is vaccine specific and dependent on the manufacturing stage. For multi-antigen vaccines, capacity estimation is complicated by the amplification of process variability, and synchronization of batch arrival and volume. Finally, we estimated that 11 vaccine manufacturing facilities staffed by approximately 8,599 fulltime employees, of whom 43% are technical personnel, would be required to achieve Africa's 2040 ambition. Overall, adopting a system-level perspective, maintaining a high, reliable, and sustainable manufacturing process yield and quality, are important when establishing new vaccine manufacturing facilities.