On 22 November 2018, the World Health Organization was informed of a cluster of suspected Yellow fever (YF) cases and deaths in Edo State, Nigeria. Edo State is located less than 400km from Lagos on a dense population movement axis between Lagos and South-Eastern Nigeria. Edo State is also a known endemic area for Lassa fever – which was initially suspected as causing the outbreak. From 22 September through 31 December 2018, a total of 146 suspected, 42 presumptive positive, and 32 confirmed cases, including 26 deaths (presumptive case fatality rate: 18%), have been reported across 15 of 18 Local Government Areas (LGAs) in Edo State (figure 1).
Blood specimens were obtained from 122 cases and sent for laboratory diagnosis; 42 (34%) samples were presumptive positive in-country based on IgM serology and sent to the regional reference laboratory, Institut Pasteur de Dakar (IPD), for confirmation. Thirty-two (76%) were confirmed by plaque reduction neutralization test (PRNT) or real-time polymerase chain reaction (RT-PCR).