ABSTRACT
<p><b>OBJECTIVE</b>To study the differences between epidemic strains of influenza virus subtype A3 circulated in China and Occident in past 18 years, in genetic level, and vaccine strains recommended by WHO in corresponding time.</p><p><b>METHODS</b>Amino acid sequences of HA1 regions of the epidemic strains, which circulated in China and Occident from 1988 to 2005, and the vaccine strains of influenza virus subtype A3 were compared by BioEdit and analyzed on the differences of HA1 and it's antigen determinants</p><p><b>RESULTS</b>Differences between epidemic strains and vaccine strains recommended in corresponding year, both in HA1 and it' s antigen determinant regions, were obviously greater than that between epidemic strains and vaccine strains recommended in next round (P< 0.01). However, differences between epidemic strains in Occident and vaccine strains recommended in corresponding year were slightly greater than that between epidemic strains and vaccine strains recommended in next round and it was not marked (P >0.05). In addition, differences between epidemic strains and vaccine strains which being used for several years, whether in China or in Occident, constantly increased accompanying the used time prolonged.</p><p><b>CONCLUSION</b>There was an obvious lag between vaccine strains recommended by WHO, analyzed in genetic level, and epidemic strains of influenza virus subtype A3 circulated in China.</p>