Seroepidemiology of Lassa virus in pregnant women in Southern Nigeria: a prospective hospital-based cohort study af Kayem, ND, Okogbenin, S, Okoeguale, J, Momoh, M, Njoku, A, Eifediyi, R, Enodiana, X, Ngwu, H, Irhiogbe, W, Ighodalo, Y, Olokor, T, Odigie, G, Castle, L, Duraffour, S, Oestereich, L, Dahal, P, Ariana, P, Gunther, S, Horby, P