Expanding modeling boundaries to design more resilient vaccine supply networks.

The COVID-19 pandemic shed light on the fragility of today's public health systems and failure to sufficiently invest in preparedness. These shortcomings are observed in delays achieving timely, equitable, and sufficient access to life-saving vaccines when faced with erratic demand. This Current Opinion describes vaccine supply networks (VSNs) from a complex adaptive systems (CAS) lens, highlighting interactions between system elements and co-evolution with the environment in which they operate. More specifically, it shows how broadening the boundaries of VSNs reveals the high degree of complexity that leads to unexpected and emergent system behavior, especially when disease threats evolve over time and across geographies. A CAS lens allows for the design of improved management strategies to ensure continued performance of VSNs during both outbreak and inter-epidemic periods, thus contributing to sustained disease management. It points to ample opportunities for more integrated modeling across disciplines to capture inherent feedback loops that influence both VSNs and disease dynamics. Furthermore, it reveals how pandemic preparedness relies on a broader understanding of the mechanisms that drive outbreak prevention and control, beyond vaccines and their direct supply chains. Finally, it highlights the value of adaptive management to navigate inevitable future disruptions and associated uncertainties, overcoming limitations of typical risk-mitigation strategies based on prediction and control.