Bayesian MCMC phylogenetic tree of 561 influenza A(H1N1)pdm09 HA sequences.

<p>The 227 Italian isolates newly characterised in this study are highlighted in red. The specific Italian clades (A–D) including more than two isolates and having a posterior probability of ≥0.9 are shown, as are two main clades including several Italian and non-Italian strains (E and F). The letters indicate the position of the identified clusters, and the scale bar the number of substitutions.