Improving the radical cure of vivax malaria (IMPROV): a study protocol for a multicentre randomised, placebo-controlled comparison of short and long course primaquine regimens by Abreha, T, Alemayehu, B, Assefa, A, Awab, G, Baird, J, Bezabih, B, Cheah, P, Day, N, Devine, A, Dorda, M, Dondorp, A, Girma, S, Hien, T, Jima, D, Kassa, M, Kebende, A, Khu, N, Leslie, T, Ley, B, Lubell, Y, Mayan, I, Meaku, Z, Pasaribu, A, Phu, N, Price, R, Simpson, J, Solomon, H, Sutanto, I, Tadesse, Y, Taylor, B, Thanh, N, Thriemer, K, von Seidlein, L, White, N, Woyessa, A, Yuentrakul, P, Zekria, R, Study Group, IMPROV