Objective: To understand the status of infants infected with influenza viruses after switch over of dominant strain in the summer of 2006.
Methods: Two groups of infants serum were collected and to be detected the antibodies of influenza viruses which the infants experienced two peaks of influenza A H1N1 circulation in the age of 3-4 and 10-11 months old and the infants only experience one circulation in 5-6 months old.
Results: The antibody of influenza A H1N1 viruses was 31.47% in the infants who experience two circulations in 3-4 months and 10-11 months old and was 26.42% which only experience circulation in the 5-6 months old. There were no significant difference between 2 groups (chi2 = 1.207, P > 0.05).
Conclusion: The group of 13 months age of infants were rarely infected influenza virus in the first time exposure at the age of < or =4 months due to maternal antibodies protection. Whenas, the group of 8 months age who were exposed at the age of > or =5 months, were more easier infected the influenza virus than the group of 13 months age in the first time exposure at the age of < or =4 months.