Objective: To study influenza epidemic and analyze antigenic and genetic characterization of the predominant strains in Wuhan area in 2003.
Methods: Epidemiological data and specimens from influenza patients were collected from surveillance sites weekly. Viruses were isolated from the specimens. Three H3 isolates were chosen to do antigenic analysis by hemagglutination inhibition (HI) test and their HA1 region was sequenced.
Results: Totally 58 influenza viruses were isolated from 418 specimens, 57 of them were identified as H3 subtype and 1 of them was B subtype; both monthly positive rate and numbers of influenza like illness had two peaks of winter and summer, the highest peak appeared in July. The 3 new H3 isolates were antigenically different from vaccine strain A/Panama/2007/99, 14 amino acid changes have been found in HA1 domain of these 3 strains compared with A/Panama/2007/99, phylogenetic analysis also confirmed the difference in HA1 domain.
Conclusions: Influenza epidemic had two peaks in Wuhan area in 2003. The activity of H3 virus was strengthened remarkably. And they are antigenically and genetically different from the vaccine strain.