Temporal changes in the net-charge and the number of NGS in HA1.

Abstract

<p>The net-charge (red circles) and the number of NGS (blue circles) in HA1 were plotted against the year of isolation for each strain of (A) A/H3N2 (<i>n</i> = 1,903) and (B) A/H1N1 (<i>n</i> = 723) viruses. The area of the circles is proportional to the frequencies of the strains, with the scales indicated at the corner. The solid and dashed lines represent the average values of the net-charge and the number of NGS in HA1 for the viruses isolated in each year, respectively.</p