Flavivirus NS1 as a pivotal virulence factor and a tractable target for next-generation antivirals, vaccines, and immunodiagnostics.

Flavivirus nonstructural protein 1 (NS1) is a secreted glycoprotein that is pivotal to viral replication and pathogenesis in dengue, Zika, yellow fever, and other flaviviral infections. Recent structural studies reveal that NS1 can adopt multiple oligomeric assemblies, switching between these states to mediate membrane remodeling and systemic immune modulation. NS1 dampens innate antiviral responses by interfering with pathogen-sensing pathways, including RIG-I/MDA5 and cGAS-STING signaling. It further subverts complement by recruiting factor H and cleaving C4, and it disrupts the endothelial glycocalyx, thereby precipitating the capillary leakage that correlates with high serum NS1 levels and severe disease. High-resolution epitope mapping has enabled the development of protective monoclonal antibodies that exploit Fc-mediated effector functions without eliciting antibody-dependent enhancement. Targeting NS1, therefore, offers exciting opportunities for next-generation vaccines, antivirals, and diagnostics. However, key knowledge gaps remain, including the role of lipoprotein-mediated trafficking, the feasibility of small-molecule inhibitors targeting NS1 oligomerization, and the optimal therapeutic window for NS1-directed interventions.