Figure 6

Average normalized codon scores for the direct 1918 human H1N1 lineage viruses, after adjusting the “ frozen” portion of the lineage ( 1976–2009) backwards in time by 21 years. The red line at 1.812 indicates the score that would be obtained from a series of proteins with the same amino acid content as those produced by H1N1, but with randomized codons.