Integrating Primary Health Care into Flexible Surge Capacity: Bridging the Subnational "Missing Middle" in Health Emergency Preparedness.

Health emergencies are governed nationally but experienced locally, where primary health care (PHC) plays a central role in maintaining essential services, surveillance, medication access, chronic disease management, communication, and recovery. Flexible surge capacity (FSC) was developed as a cross-sector approach for identifying and preparing additional personnel, facilities, supplies, systems, and community capabilities, but PHC has not been explicitly integrated into the concept. This narrative conceptual review examined how emergency-ready PHC can be incorporated into FSC at the subnational level. The literature identification followed two complementary streams: one addressing PHC and health-emergency preparedness and another concept-directed stream addressing the foundational and subsequent FSC literature. Following relevance screening, 31 core publications were retained for conceptual synthesis. The two evidence streams were compared to identify functional convergence, required adaptations, governance and clinical safeguards, activation considerations, and evidence gaps. The resulting framework positions PHC as defining essential functions that should be sustained during emergencies, while FSC provides additional cross-sector capability when routine functional capacity becomes insufficient. The proposed PHC-integrated FSC model therefore represents a continuity-and-surge approach rather than solely an expansion of acute-care capacity. The model is conceptual, and its downstream effects should be regarded as hypotheses for future evaluation rather than established effectiveness claims. PHC-integrated FSC should complement, not replace, adequately resourced routine PHC and existing emergency-response systems.