Background. Our objective was to determine the serological signals that indicated the possible dominant circulating influenza virus subtypes for the coming influenza seasons. Methods. Healthy children 6 months through 5 years of age, adults 18-60 years of age, and elderly adults >60 years of age were recruited to receive seasonal trivalent inactivated influenza vaccinations from October through December during the 2006-2007 and 2008- 2009 seasons. Paired serum samples were collected at baseline and at 3 weeks after vaccination. Using a hemagglutination inhibition (HAI) assay, we measured antibody responses to local influenza strains circulating early in October, before each winter influenza season. Results. A total of 301 subjects were tested for antibody to local strains (80, 120, and 101 subjects in the 2006-2007, 2007-2008, and 2008-2009 seasons, respectively) . The dominant winter influenza strains in Taiwan were B/ Malaysia/2506/ 2004-like in the 2006-2007 season, A/Brisbane/ 59/2007-like virus (H1N1) in the 2007-2008 season, and A/ Brisbane/59/2007-like virus (H1N1) in the 2008-2009 season. The group with the lowest number of subjects with an HAI titer of >= 40 at baseline was children with antibody against the B/ Taiwan/0050/2006 in the 2006-2007 season, A/ Taiwan/785/2006 (H1N1) in 2007-2008 season, and A/Taiwan/951 /2007 (H1N1) in 2008-2009 season. The emergence of these viruses correlated well with the circulating influenza subtype in the following winter peak seasons. Conclusions. Low seroprotection rate among children against a specific locally circulating influenza strain might predict the dominantly circulating subtype of influenza virus in the coming winter season. A year-end preseasonal serological survey of children could provide valuable information about the possible circulating strain and tailor the disease- control strategy accordingly. ; 附設醫院檢驗醫學部 ; 醫學院附設醫院 ; 期刊論文