Enable 1.5
Aiming to fill knowledge gaps identified in Enable 1.0 (see above), CEPI is coordinating the continuation of the study under Enable 1.5, focusing on Lassa fever at five sites in Liberia (one site), Nigeria (three sites), and Sierra Leone (one site). Over 5,000 participants were recruited from Lassa fever hotspots and followed for 12 months. Enable field staff teams assessed participants’ symptoms every 2 weeks and drew blood every 3 months for serological (antibody) testing. Suspected Lassa fever cases underwent thorough evaluations, including clinical assessments and laboratory testing including RT-PCR and malaria blood smear microscopy. Data aggregation, cleaning, and analysis are underway, while serological testing is also beginning.
Mid-Term Site Visits - Progress and Insights
In June 2025, CEPI's Enable 1.5 team, in collaboration with MMARCRO, IVI, and MRC Gambia, conducted mid-term site visits across the three participating countries. The valuable field trip began in Kenema, Sierra Leone, continuing through to Phebe, Liberia, and concluding in Abuja, Nigeria. In October 2025, CEPI and partners (IVI, NCDC, Epicentre and MMARCRO) visited Enable 1.5 sites in Edo, Ondo, and Abakaliki States in Nigeria. The team reviewed scientific progress and deliverables, while also evaluating laboratory and clinical infrastructure, and troubleshooting as needed. All sites were progressing with the study as expected. Discussions highlighted the crucial role of sustained and enhanced community engagement to mitigate participant attrition, as well as continuous communication regarding the impact of Enable’s capacity-strengthening efforts.
  
Study expands to Bauchi State
Bauchi State, northeastern Nigeria, reports one of the highest Lassa fever burdens in the country, along with Edo and Ondo States. In April 2026, the Enable 1.5 study expanded to include Bauchi State, commencing enrollment of 1000 patients for follow up over 12 months. The case definition used allows for the identification of infections with and without fever to ensure all disease presentations are captured, and an accurate incidence rate is measured; the current case definition also prioritizes epidemiological linkage to confirmed cases. As in other sites already in Enable 1.5 (Edo, Ondo, and Ebonyi States), participants will give blood samples for RT-PCR and ELISA analyses. Follow-up is currently ongoing, with data entry expected to finish in mid-2027, followed by data tidying and analysis, and the publication of results. CEPI is grateful to be collaborating with ATBUTH and NCDC in this important study expansion.
Sociobehavioural study (SBS) commenced
The Enable 1.5 Socio-Behavioural Study has commenced, assessing community attitudes and acceptance of vaccination with a future licensed Lassa fever vaccine, and participation in Lassa fever vaccine and therapeutics clinical trials in West Africa. The SBS is being conducted across six sites in three countries – Nigeria (four sites), Liberia (one site), and Sierra Leone (one site). A Training and Harmonisation Workshop was held on 1–2 April 2026 to align the four Nigerian sites and key partners ahead of the implementation of the Socio-Behavioural Study. It provided a practical forum to clarify the study approach, confirm site-level expectations, and support readiness for field activities.
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In Enable 1.0 over 23,000 participants were followed up in 2019–2023 to estimate the incidence of Lassa fever infection and disease across five West African countries (Benin, Guinea, Liberia, Nigeria, and Sierra Leone). Preliminary results indicate that Lassa fever baseline seroprevalence — a measure of the proportion of people who have antibodies against Lassa virus at a given time, indicating previous exposure — was around 30%, ranging from 2% in Benin to 48% in Liberia. During the study, 39 cases of symptomatic Lassa fever were observed. The results of this study are soon to be published. 
