Fig. 2.

(A) Starting from publicly available HA viral sequences, a posterior distribution of the estimated TMRCA was derived using a Bayesian coalescent model, which assumes exponential population growth (coded in BEAST 1.4), with the date of the first known human case highlighted. Details of the BEAST analysis and parameter estimates are presented in (8). Posterior distribution of the doubling time of the epidemic (B) and of R₀ (C). The bar charts show the results obtained from the first 11 sequences available on 2 May 2009 (orange) and from an updated analysis with 23 epidemiologically unlinked sequences available on 7 May 2009 (blue). The differences in estimates arise due to some sequences in the smaller sample being from epidemiological clusters, highlighting the importance of careful sampling.