FIG. 2.

Host adaptedness values for a series of different virus sequences, including avian (black), human (red), classical swine (blue), Eurasian swine (cyan), and the host-shift sequence (orange). Open red circles represent post-1977 human H1N1 viruses whose isolation times were corrected as described in the text. Error bars for the host-shift sequence represent the 95% CI indicating the uncertainty in the ancestral reconstruction. For PA and PB2, we additionally include triple-reassortant swine sequences (green). 1918 and pandemic H1N1 2009 sequences are labeled. Human sequences inside the distribution of avian sequences represent sporadic H5N1 infections.