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.
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.
  
End of Study Activities
Participant follow-up has been completed, and study closeout is underway for Enable 1.5 sites in Liberia, Sierra Leone, and Nigeria. Data aggregation, cleaning, and analysis are ongoing, while serological testing activities continue. Following completion of laboratory analyses and data validation, final analyses will be conducted and results disseminated through reports, publications, and stakeholder engagement activities.
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, enroling 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 give blood samples for RT-PCR and ELISA analyses. Follow-up is currently ongoing, with data entry expected to finish in mid-2027, after which data cleaning, analysis, and publication activities will proceed. CEPI is grateful to be collaborating with ATBUTH and NCDC in this important study expansion.
Sociobehavioural study (SBS) completed
The Enable 1.5 Socio-Behavioural Study has been completed, assessing community attitudes towards vaccination with a future licensed Lassa fever vaccine, and participation in Lassa fever vaccine and therapeutics clinical trials in West Africa. The study was conducted across six sites in three countries – Nigeria (four sites), Liberia (one site), and Sierra Leone (one site). Data cleaning and analysis are underway, and a comprehensive report summarizing findings and recommendations will be shared following completion of all analyses.
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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 being published. 
