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Lassa Fever Burden and Reported Case Fatality in Nigeria from 2024 To Epidemiological Week 31 Of 2026: The Public Health Lessons

Aaron Umasoye Udogadi, Agwu Michael Ezenna, and Stella Okwelle PC,

Abstract

Background: Lassa fever remains an important public health challenge in Nigeria. We assessed changes in reported disease burden, geographical distribution and case fatality between 2024 and epidemiological week 31 of 2026. Methods: We conducted a retrospective descriptive analysis of aggregate national surveillance data from Nigeria Centre for Disease Control and Prevention Lassa fever situation reports. Indicators included suspected and confirmed cases, deaths among confirmed cases, the confirmed- to-suspected case proportion, and affected states and local government areas. Case-fatality ratios were calculated with Wilson 95% confidence intervals . Exploratory two-sided pooled two-proportion z-tests compared CFRs. Epidemiological weeks 1–31 of 2025 and 2026 were compared to reduce bias from unequal observation periods. Results: Confirmed cases decreased by 12.3%, from 1,309 in 2024 to 1,148 in 2025, whereas deaths remained similar at 214 and 215. CFR increased from 16.35% (95% CI 14.44–18.45%) to 18.73% (16.58–21.09%; p = 0.121). By week 31 of 2026, 1,017 confirmed cases and 239 deaths were reported, yielding a CFR of 23.50% (21.00–26.20%). Compared with weeks 1–31 of 2025, confirmed cases increased by 21.7% and deaths by 53.2%; CFR increased from 18.66% to 23.50% (p = 0.011). The 2026 report attributed approximately 86% of confirmed cases to Ondo, Bauchi, Taraba, Edo and Benue. Conclusion: Reported Lassa fever fatality increased in early 2026, including in a comparison of equivalent surveillance periods. These findings support strengthening timely diagnosis, referral, supportive care and outcome surveillance, particularly in high-burden states. Aggregate data cannot establish the causes of the increase.

References

1. Nigeria Centre for Disease Control and Prevention. Lassa fever situation report. Epidemiological week 52, 2024. https://ncdc.gov.ng/themes/common/files/sitreps/a45a720bd6ddd1e75a5a3e7e6195e412. pdf 2. Nigeria Centre for Disease Control and Prevention. Lassa fever situation report. Epidemiological week 52, 2025. https://zadmin.ncdc.gov.ng/themes/common/files/sitreps/04beb529df54f4ceb99ac291842 640b4.pdf 3. Nigeria Centre for Disease Control and Prevention. Lassa fever situation report. Epidemiological week 31, 2026. https://ncdc.gov.ng/themes/common/files/sitreps/a373aae5ca8b3ff2346793d5bbed5cbb.p df 4. Duvignaud A, Jaspard M, Etafo IC, et al. Lassa fever outcomes and prognostic factors in Nigeria (LASCOPE): a prospective cohort study. Lancet Glob Health. 2021;9(4):e469–e478. doi:10.1016/S2214-109X(20)30518-0. 5. World Health Organization. Lassa fever. https://www.who.int/news-room/fact- sheets/detail/lassa-fever (accessed 25 October 2026). 6. Nigeria Centre for Disease Control and Prevention. Weekly Epidemiological Report. Volume 15, number 52. Week 52, 2025. https://ncdc.gov.ng/themes/common/docs/wers/661_1772120299.pdf IJMEPR Supplementary Table S1 State distribution of Lassa fever cases in 2024 State or FCT Suspected Confirmed National case share % Confirmation % Abia 20 0 0.00 0.00 Adamawa 21 3 0.23 14.29 Akwa Ibom 8 0 0.00 0.00 Anambra 47 4 0.31 8.51 Bauchi 1,143 253 19.33 22.13 Bayelsa 27 2 0.15 7.41 Benue 1,072 64 4.89 5.97 Borno 13 0 0.00 0.00 Cross River 64 8 0.61 12.50 Delta 100 5 0.38 5.00 Ebonyi 382 53 4.05 13.87 Edo 3,103 289 22.08 9.31 Ekiti 17 0 0.00 0.00 Enugu 126 15 1.15 11.90 FCT 76 2 0.15 2.63 Gombe 64 5 0.38 7.81 Imo 41 3 0.23 7.32 Jigawa 26 2 0.15 7.69 Kaduna 127 15 1.15 11.81 Kano 58 1 0.08 1.72 Katsina 24 1 0.08 4.17 Kebbi 8 0 0.00 0.00 Kogi 158 37 2.83 23.42 Kwara 10 0 0.00 0.00 Lagos 49 1 0.08 2.04 Nasarawa 72 5 0.38 6.94 Niger 13 3 0.23 23.08 Ogun 39 1 0.08 2.56 Ondo 2,613 400 30.56 15.31 Osun 8 0 0.00 0.00 Oyo 41 1 0.08 2.44 Plateau 115 17 1.30 14.78 Rivers 75 6 0.46 8.00 Sokoto 10 0 0.00 0.00 Taraba 301 112 8.56 37.21 Yobe 24 1 0.08 4.17 Zamfara 3 0 0.00 0.00 Nigeria 10,098 1,309 100.00 12.96 Source: cumulative state table in the 2024 week-52 report [2]. State rows were checked against the primary table and the national totals recalculated. Zero confirmed cases means no reported confirmed case in this table, not demonstrated absence of infection.

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