Table 1 Comparing drift of H2, H3, and H1 human influenza virus HAs by amino acid identity.
SubtypeComparisonAmino acid identity (%)
H3N2HK/68 versus Wisc/05*87
H1N1USSR/77 versus SI/2006 HA*91
H2N2Sing/57 versus Alb/6794

*H3N2 and H1N1 strains recommended by the World Health Organization for use in 2007 to 2008 Northern Hemisphere vaccine were used for sequence comparison.