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Graphical distribution maps of human influenza A/H3N2 viruses in (A) 2008 and (B) 2009. The balloons containing a residue exhibiting maximum frequency at the 158th site are dark colored, while the other cases are light-colored. The size of the balloons are varied with the size of the sequence: small (No <=10), medium (10<No<50), and large (No>50).
