Epidemiological and Virological Features of Yellow Fever Outbreaks in North Central Nigeria: A Multi-State Analysis

Yellow fever virus (YFV), a mosquito-transmitted flavivirus, caused a major outbreak across Nigeria between 2017 and 2020, with North Central states including Kwara, Kogi, and Niger disproportionately affected. A systematic multi-state virological and epidemiological analysis of these outbreaks remains unpublished, representing a significant knowledge gap. This study conducts a retrospective multi-state epidemiological and virological analysis of confirmed yellow fever cases in Kwara, Kogi, and Niger states from 2018 to 2024 using NCDC outbreak investigation data and archived diagnostic samples. Case count, attack rate, case fatality rate, age and sex distribution, and seasonal outbreak timing will be analysed for each state. Archived serum samples from PCR-confirmed YFV cases will be retrieved from the NCDC Reference Laboratory and subjected to full-length genome sequencing by Illumina next-generation sequencing. Phylogenetic analysis will classify detected strains within YFV genotypes and assess relatedness between outbreaks in different states. Vaccination coverage data from preventive and reactive vaccination campaigns will be overlaid against case distribution maps. Prior North Central outbreak reports relied predominantly on serological data without genomic characterisation, limiting understanding of outbreak origins and spread. Findings will generate the first comprehensive virological and epidemiological portrait of yellow fever in North Central Nigeria, informing NCDC and the Global Yellow Fever Initiative's risk stratification and vaccination planning frameworks. Keywords: yellow fever virus, outbreak analysis, North Central Nigeria, genomics, vaccination coverage