Objective To study influenza activity and antigenic characterization in Guangdong during 2003.Methods The data of influenza surveillance were utilized.Antigenic analysis was performed by using cross hemagglutination inhibition test.The gene of hemagglutinin(HA1)protein were amplified by RT-PCR.PCR products were purified and sequenced.Finally,the sequence data were analyzed with Megalign and Editseq software.Results Of the 510 positive isolates,481(92.4) were in fluenza A(H3N2) viruses,29(7.6%)were influenza...