Early Warning Systems for Health Security: A Systematic Review of Surveillance System Design, Implementation, and Impact

Abstract

Early warning systems (EWSs) represent critical infrastructure for detecting, monitoring, and responding to public health threats. This systematic review analyzes the design features, implementation challenges, and measured impacts of health surveillance systems deployed globally over the past decade. Through comprehensive database searches, 47 eligible studies were identified that evaluated diverse EWS implementations across various geographical contexts and threat domains. Analysis revealed four predominant EWS architectural approaches: indicator-based surveillance, event-based surveillance, syndromic surveillance, and integrated systems. Key design elements supporting effective implementation included interoperability with existing health information infrastructure, scalable technological platforms, and adaptable alert algorithms. Implementation barriers consistently identified included inadequate human resource capacity, technological infrastructure limitations, fragmented governance structures, and insufficient sustained funding mechanisms. Documented impacts included reduced detection time for outbreaks (average reduction of 7.4 days), improved response coordination, and enhanced situational awareness among decision-makers. However, rigorous impact evaluations using standardized metrics remain limited. The review identifies critical gaps in current research, particularly regarding cost-effectiveness analyses, sustainability assessments, and implementation studies in resource-constrained settings. Recommendations include developing standardized evaluation frameworks, prioritizing user-centered design approaches, investing in workforce capacity development, and establishing sustainable financing mechanisms. This systematic analysis provides a comprehensive evidence base to guide future EWS design, implementation, and evaluation efforts in advancing global health security.