Figure 3.

Reassortment leading to emergence of the 2009 pandemic H1N1 virus.A, cartoon schematic of various swine lineages contributing gene segments to the novel virus (adapted from data in Garten et al. (2009) (24)). B, conservation of key humanizing receptor-binding variants in example viruses from the original 1918 pandemic, through the classical swine H1N1 lineage, and within both pre- and post-2009 human H1N1 strains. Strain abbreviations are: A/Brevig Mission/1/1918, A/swine/Indiana/P12439/2000 (nearest identified swine HA gene precursor to 2009 human pandemic strains), A/Solomon Islands/3/2006 (pre-2009 seasonal), and A/California/04/2009 (2009 pandemic).