Assessment of immunity against Yellow Fever virus infections in northeastern Nigeria using three serological assays.

Introduction Poor systematic surveillance for Yellow Fever virus (YFV) is primarily due to lack of affordable diagnostic facilities in resource constrained countries. Objectives This study aimed at providing evidence- based information on immunity against Yellow Fever with a view to assessing the possibility of the recent epidemics persisting in Nigeria. Methods Six hundred patients with febrile illness seeking malaria test in selected hospitals were tested for YFV antibody using three serological assays: IgM, Microneutralization test (MNT90 ) and Plaque reduction neutralization test (PRNT90 ). Results The three assays commonly detected YFV antibody (Ab) in 1.7% patients, MNT: IgM in 8.3%, IgM: PRNT in 7.1% and MNT: PRNT in 3.2%. Immunity against YF was significantly higher in Bauchi and Borno than Adamawa and children aged 0-9 years compared 20-29 years. YFV neutralizing antibody (nAb) strongly correlated with vaccination status of the patients. More unvaccinated patients had nAb compared with the vaccinated. Immunity against YF among treated patients with antibiotic and/or anti-malaria before sample collection inversely correlated with the untreated. YVnAb among unvaccinated indicates natural infections. Conclusion Acute YFV infections were mistaken for malaria and natural infections are ongoing. Individuals aged ≥20 should be targeted during mass vaccination campaigns. With low population immunity, repetitive YF epidemics in Nigeria is not yet over. The current policy on Yellow Fever vaccination in Nigeria still leaves a large unimmunized population at the risk of epidemics. Sufficient mass vaccination in combination with National Programme on Immunization remains key to averting YF epidemics. This article is protected by copyright. All rights reserved.