Figure 1

Mutation accumulation within the 2009 A/H1N1 influenza strain during the course of the 2009/2010 flu season. The earliest sequenced genotype (California/04/2009) was used as the baseline for comparison with all subsequent genotypes (mutation counts reflect divergence from that starting sequence). The vertical red line indicates the date the reference sequence was collected. This sequence is not included because it, by definition, has a mutation count of zero and ignores contemporaneous sequence variation.