P-2326. The Under-recognized Burden of Lassa Virus Infection in Liberia

Abstract Background Lassa virus (LASV) is a persistent and lethal threat in endemic regions of West Africa. While severe disease due to Lassa fever (LF) is responsible for 5000-10,000 deaths annually, there is evidence of a wide spectrum of clinical manifestation of LASV infection. Methods The Coalition for Epidemic Initiative (CEPI) sponsored ENABLE study is a prospective, observational, cohort study of the prevalence and incidence of LASV infection and LF in five West African countries: Nigeria, Liberia, Sierra Leone, Guinea, and Benin. LASV seroprevalence was determined by LASV nucleoprotein (NP) IgG at entry (ReLASV NP IgG ELISA). Participants were assessed every 2 weeks in-person for fever with and without LF symptoms. Febrile events triggered LASV RT-PCR (RealStar Lassa Virus RT-PCR Altona 2.0). To assess for subclinical LASV infection, serum was collected every 6 months for 2 years from a subset (Infection Cohort) for LASV NP IgG. Results In Liberia, 5,005 were enrolled between April 2021 and December 2023; 25 withdrew before data collection. Of the remaining 4,980 participants, 1,018 were in the Infection Cohort and 591 of these provided samples at all 5 time points. At entry, 2,259 (45%) were LASV NP IgG positive. Entry LASV NP IgG seropositivity increased with age with the lowest prevalence among those 2-5 years (101 of 510, 20%, CI: 17-24%) rising to a peak among participants 30-39 years (322 of 564, 57%, CI: 53-61%). Of the 591 with serological results at all 5 timepoints, 314 (53%) were LASV NP IgG negative at study entry and 68 (22%) had at least a single change in serostatus from seronegative to seropositive. Over 24-months, 1,176 febrile events in 818 participants were identified and of these 10 (1%) had LASV RNA detected. Conclusion In this 24-month longitudinal study of individuals in a LASV hyperendemic area of West Africa, close to half were LASV seropositive at enrollment, and across two years of follow-up, 1 in 5 participants who were LASV seronegative at entry had observed seroconversion. However, only a small number of LF cases (n=14) were identified through symptom-driven testing dependent on fever. These findings indicate that in this region of Liberia LASV infection is common, increases during the first decades of life, but is rarely clinically detected. Disclosures Katie R. Mollan, MS, Gilead Sciences: Grant/Research Support|Ridgeback Biotherapeutics: Grant/Research Support