Notably, for the PB1,HA and M genes, some of these newly generated sequences are more similar to the S-OIV epidemic than any previously reported isolates (Supplementary Fig. A14-3). Notably, seven out of eight genomic segments found in a single 2004 isolate (Sw/HK/915/04 (H1N2)) were located in a sister lineage to the current outbreak. Not only does this suggest that the precursors of S-OIV were swine viruses, but also that they were geographically widely distributed. Crucially, however, the observation of a sister relationship between the current outbreak virus and Sw/HK/915/04 cannot be interpreted as evidence for a Eurasian origin of the outbreak, owing to the long branch of the phylogeny leading to the 2009 human strains (Fig. A14-2 and Table A14-1). This

FIGURE A14-2 Genetic relationships and timing of S-OIV for each genomic segment. Symbols represent sampled viruses on a timescale of when they were sampled and coloured by host species (pigs, red; humans, blue; birds, green). Internal nodes are reconstructed common ancestors with 95% credible intervals on their date given by the red bars. The S-OIV outbreak strains are represented by a blue triangle, with the apex representing the common ancestor of these.