Development of a broad-lineage Lassa virus rapid diagnostic test informed by the WHO REASSURED framework.

Lassa fever is a high-risk viral disease endemic to West Africa for which rapid and reliable diagnosis is essential for outbreak control. Here, we describe the development of a lateral flow-based rapid diagnostic test (RDT) targeting the Lassa virus nucleoprotein using newly generated monoclonal antibody pairs. The analytical performance of the assay was evaluated using human serum and plasma specimens as well as inactivated Lassa virus strains and compared with a commercially available antigen test. The final RDT (Pair 2; 1P-44-7/9B-28) demonstrated high analytical sensitivity and 100% specificity across 60 human samples and detected multiple genetically diverse Lassa virus strains, with lineage-dependent differences in analytical sensitivity. In direct analytical comparisons using recombinant antigen, the assay was approximately 64-fold more sensitive than the ReLASV Pan-Lassa Antigen Rapid Test. The RDT provides a rapid visual readout, remains stable at ambient temperatures, and is suitable for decentralized testing workflows, features aligned with key aspects of the World Health Organization (WHO) REASSURED framework. These results indicate that the developed RDT offers a robust and broadly reactive platform for Lassa virus antigen detection and has potential utility for surveillance and outbreak response in resource-limited settings.IMPORTANCELassa fever remains a significant public health concern in West Africa, where diagnostic capacity is often limited in endemic regions. This study describes the development of a broad-lineage Lassa virus rapid diagnostic test informed by the World Health Organization (WHO) REASSURED framework. The assay demonstrates high analytical sensitivity and broad lineage coverage in a field-deployable format, supporting its potential utility for early case detection and decentralized surveillance in endemic settings.