Comparison of the percentages of the pH1N1-E374K mutants in HA2 and other variants at the four antigenic sites and their relationships with different intervention strategies in various epidemic periods, 2009–2010.

1. The effect of intervention of antiviral agent on the percentages of E374K mutants: Before (0%, 0/17) vs after (40.78%, 73/179), p2. The effect of intervention of vaccination on the percentages of E374K mutants: Before (22.86%, 32/140) vs after (72.34%, 41/56), p3. The effect of intervention of antiviral agent on the percentages of the pH1N1 variants with substitutions at four antigenic sites (Ca, Cb, Sa, Sb): Before (29.41%, 5/17) vs after (17.83%, 28/157), p = 0.324 (Fisher's exact test).4. The effect of intervention of vaccination on the percentages of the pH1N1 variants with substitutions at four antigenic sites (Ca, Cb, Sa, Sb): Before (11.86%, 18/118) vs after (25%, 15/56), p = 0.097 (Fisher's exact test).*: Two strains with double mutations in Ca and Sa sites.**: Three strains with double mutations in Ca and Sa sites.