A sero-epidemiology study was carried out in one urban city (Taichung city) and one rural county (Nantou) in central Taiwan starting before the 2008 fall influenza season in Taiwan and through the beginning of 2010. Households with schoolchildren were recruited for the study and followed sequentially, with serum samples were taken in several pre-season and post-season sampling periods for haemagglutination inhibition (HI) assay against H1N1 viruses of seasonal vaccine, wild- type, and pH1N1 strains. Survey questionnaires regarding their contact patterns, social demographic characteristics, and influenza-like symptoms during the flu seasons are obtained. Using serologic evidence of infection, i.e., 4-fold increase in HI titers, we investigate the temporal changes in pH1N1 infections among this cohort, as well as transmission heterogeneity due to age, household type/size, location, status of vaccination, etc.