Retaining Participants in a Prospective Epidemiological Study Involving Blood Draws Through Sustained Engagement: Lessons from Enable 1.0 Incidence Study on Lassa Fever Infection in Abakaliki, Southeast Nigeria

Background Participant retention is critical in longitudinal studies involving blood draws. Enable 1.0 Incidence Study on Lassa Fever was conducted to estimate Lassa virus infection and disease to inform outbreak preparedness and vaccine research. This nested analysis aimed to explore community engagement strategies employed to retain participants. Methods Enable 1.0 was a multi-site, multi-country, prospective cohort study (December 2020–December 2023) aiming to estimate the incidence of Lassa virus infection and symptomatic Lassa fever disease. In Abakaliki Nigeria, the study tracked Lassa virus seroconversion among 1,000 healthy participants across 10 communities in three Local Government Areas. Community Liaison Officers, village guides, and field workers sustained engagement through fortnightly visits and sensitization meetings. Fieldworkers completed a semi-structured Google Forms questionnaire documenting their experiences and observations across 713 participants, including participant reception, retention threats, and their engagement strategies. The data were analyzed descriptively using IBM-SPSS Statistics Version-25. Results Overall, the study achieved a 90.5% participant retention rate over the 24-month follow-up period across the full cohort of 1,000 participants. Based on fieldworker reports covering 713 participants, 91.4% (652/713) completed the study, while 8.6% (61/713) did not. Reported retention threats (102/713; 14.3%) included inadequate compensation (52/713; 7.3%), family pressure (48/713; 6.7%), and fear of blood rituals (37/713; 5.2%). Reasons for non-completion were relocation (23/713; 3.2%), refusal (15/713; 2.1%), family opposition (6/713; 0.8%), and death (6/713; 0.8%). Key retention strategies included engaging village guides (439/713; 61.6%), incentives (293/713; 41.1%), family support (152/713; 21.3%), and involvement of traditional leaders (151/713; 21.2%). Despite rumours related to blood rituals, sustained community engagement and unscheduled home visits supported by reassurance from the study technical team helped dispel misinformation, with 88.2% (629/713) of participants remaining warmly receptive to fieldworkers throughout the study. Conclusion The Enable 1.0 study demonstrated that high participant retention is achievable in resource-limited high-risk settings when structured community engagement and rapid response mechanisms are integrated into study implementation. Future studies should embed engagement structures, institutionalize rapid responses to rumours, and prioritize transparent communication to strengthen retention and public trust.