Pandemic H1N1 virus transmission and shedding dynamics in index case households of a prospective Vietnamese cohort by Thai, P, Mai, L, Welkers, M, Hang, N, Thanh, LT, Dung, V, Yen, N, Duong, T, Hoa, L, Thoang, D, Trang, H, Jong, d, Wertheim, H, Hien, N, Horby, P, Fox, A