Prospective cohort study to evaluate Lassa fever incidence, symptoms and coinfection with malaria in West Africa: the Enable Lassa Research Programme ('ENABLE 1.5') - study protocol.

INTRODUCTION

Lassa fever (LF), a viral haemorrhagic disease, poses a significant public health challenge in West Africa. Lassa virus infection frequently causes mild malaria-like symptoms, potentially leading to misdiagnosis and an underestimated burden. Severe LF can lead to multi-organ failure, and survivors may experience sensorineural hearing loss (SNHL). Building on the contributions of the Enable Lassa Research Programme (ENABLE 1.0), which ran in West Africa from 2020 to 2024, ENABLE 1.5 aims to further address gaps in understanding LF disease burden to inform future late-stage vaccine trials. The study will assess the incidence of symptomatic reverse transcription (RT)-PCR-confirmed LF disease, including malaria coinfection.

METHODS AND ANALYSIS: The ENABLE 1.5 prospective cohort study will be conducted across five study sites: one in Liberia, three in Nigeria and one in Sierra Leone. Stratified cluster sampling will identify eligible individuals at the household level from communities either involved in ENABLE 1.0 or identified through recent LF surveillance as hotspots. A total of 5000 participants will be recruited, 1000 per study site (minimum) and equally stratified in the following ages: 0-5, 6-10, 11-17, 18-50 and >50 years. All participants will be followed up for 12 months. Baseline data collection will gather key variables and blood specimens from all participants, with baseline SNHL prevalence assessed at three study sites. Active follow-up of all participants will involve symptom assessments every 2 weeks and blood draws every 3 months for serological testing (IgG). Suspected LF cases will undergo thorough evaluations, including malaria rapid diagnostic testing, clinical assessments and laboratory testing, including RT-PCR and malaria blood smear microscopy.