Figure 3. Dynamic changes of amino acid residues at the antigenic sites of pH1N1-HA in Taiwan, 2009–2010.

<37th Week: Pre-peak period of the 2009 epidemic; 37th Week: Peak of the 2009 epidemic; >37 ^th Week: Post-peak period of the epidemic; Green background: Pre-peak period of the epidemic ; Yellow background: Post-vaccination campaign phase; Strains with red color: pH1N1 strains were isolated from severe cases.