Objective To understand antigenic and genetic characteristics of HA_1 gene of influenza A circulated in Guangdong in 2003.Method The data of influenza molecular surveillance were analyzed.481 influenza A(H3N2) viruses were isolated.Most of influenza A(H3N2) viruses were antigenically distinct from vaccine strain A/Panama/2007/99(H3N2),and similar to a drift variant stain,A/Fujian/411/02(H3N2).Compared with vaccine strain A/Panama/2007/99(H3N2),there were 25-30 amino acid substituted on HA_1 protei...