Lassa virus live tracking and lineage assignment: how nextstrain can enhance surveillance and public health in Africa and beyond.

Lassa virus (LASV), a zoonotic, bi-segmented arenavirus endemic to West Africa, causes seasonal epidemics with substantial morbidity and mortality. Increasing frequency of exported cases emphasizes the need for near real-time genomic surveillance to support outbreak response and clinical decision-making. We developed a suite of open-access resources on the Nextstrain and Nextclade platforms tailored to LASV. These include live phylogenetic and phylogeographic visualization, as well as Nextclade builds for rapid mutation detection and lineage assignment based on the L and S segments and the glycoprotein complex (GPC). A dedicated GPC phylogeny enables tracking of clinically relevant mutations, including immunologically relevant variants such as alanine at position 76 (A76), which is prevalent in lineage II and is implicated in reduced binding of monoclonal antibody 25.10C. The Nextclade tools distinguish LASV from other mammarenaviruses and assign lineages with Matthews correlation coefficients exceeding 85%. These tools are available at https://nextstrain.org/lassa for immediate use in surveillance, data annotation, outbreak response, and potentially support clinical decision-making in both endemic regions and exported-case scenarios. A key limitation is dependence on genomic data quality and recency. Although sampling-to-submission delays have decreased over the past 40 years, the average delay in the past five years remains ∼2 years. In many endemic LASV regions, challenges, such as limited resources, infrastructure, and previous experiences of stigmatization and political repercussions linked to outbreak reporting, restrict data sharing. The resulting disparities and delays may hinder comprehensive surveillance and timely response, with implications for global public health.