Community engagement, social context and coverage of mass anti-malarial administration: comparative findings from multi-site research in the Greater Mekong sub-Region by Pell, C, Adhikari, B, Myo Thwin, M, Kajeechiwa, L, Nosten, S, Nosten, F, Sahan, K, Smithuis, F, Nguyen, T, Hien, T, Tripura, R, Peto, T, Sanann, N, Nguon, C, Pongvongsa, T, Phommasone, K, Mayxay, M, Mukaka, M, Peerawaranun, P, Kaehler, N, Cheah, P, Day, N, White, N, Dondorp, A, Von Seidlein, L