Effect of a serogroup A meningococcal conjugate vaccine (PsA-TT) on serogroup A meningococcal meningitis and carriage in Chad: A community study by Daugla, D, Gami, J, Gamougam, K, Naibei, N, Mbainadji, L, Narbé, M, Toralta, J, Kodbesse, B, Ngadoua, C, Coldiron, M, Fermon, F, Page, A, Djingarey, M, Hugonnet, S, Harrison, O, Rebbetts, L, Tekletsion, Y, Watkins, E, Hill, D, Caugant, D, Chandramohan, D, Hassan-King, M, Manigart, O, Nascimento, M, Woukeu, A, Trotter, D, Stuart, J, Maiden, M, Greenwood, B