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(9214)were in fluenza A(H3N2)viruses, 29 (7.6%)were influenza B viruses.52 outbreaks were confirmed by lab, including 50 due to influenza A(H3N2)viruses and 2 due to influenza B viruses. Most of influenza A(H3N2)viruses were similar antigenically to A/Fujian/411/02(H3N2), a drift variant of vaccine strain A/Panama/2007/99(H3N2). There were 25 different amino acid on HA1 domain and the homology of amino acid sequence was 92.1% when compared current strains in Guangdong with waccine strain A/Panama/2007/99(H3N2);28 of the influenza B viruses belonged to the B/Ⅴ ictoria lineage and were similar antigenically to the vaccine strain B/HongKong. 1 influenza B virus belonged to the B/Yamagata.

  Conclusion   In Guangdong, influenza activity in 2003 was stronger than that in 2002;influenaz A(H3N2)and two lineages of influenza B were co-circulating. The predominant viruses were subtype of influenza(H3N2). And the antigenic drift of influenza(H3N2)occurred.