Fig. 3. Forward simulations estimating the timing of the index case in Hubei province.

(A) Days between index case infection and stable coalescence in forward compartmental epidemic simulations (n = 1000). (B and C) Days between index case infection and stable coalescence after rejection sampling (B) and posterior distribution for date of index case infection (C), conditioned on an ascertained case by 17 November 2019, which is denoted by a long-dashed line. (D and E) Epidemic simulation, conditioned on an ascertained case by 1 December 2019, which is denoted by a short-dashed line. (F to H) Two-phase epidemic (F) days between index case carrying less-fit variant and adaptation (n = 2000), (G) days between adaptation and stable coalescence (n = 1000), and (H) posterior distribution for date of index case infection, conditioned on an ascertained case by 17 November 2019. (I to K) Two-phase epidemic conditioned on an ascertained case by 1 December 2019. Gray dashed lines indicate median estimates.