New Variants and Age Shift to High Fatality Groups Contribute to Severe Successive Waves in the 2009 Influenza Pandemic in Taiwan

摘要: Past influenza pandemics have been characterized by the signature feature of multiple waves. However, reasons for waves in a pandemic are not understood. Successive 2009 pandemic, with sharp increase hospitalized and fatal cases, occurred Taiwan during winter 2010. In this study, we sought to discover possible contributors pandemic. We conducted large-scale analysis 4703 isolates an unbiased manner monitor emergence, dominance replacement various variants. Based on data from surveillance epidemic curves each variant clade, defined virologically temporally distinct May April 2011 as 1 2, interwave period wave 3. Except 3, was dominated one variant. three variants emerged co-circulated, formed phylogenetic clades, based hemagglutinin (HA) genes other segments. The severity represented case fatality ratio (CFR) cases. CFRs 3 were 6.4%, 5.1%, 15.2% 9.8%, respectively. results highlight association virus evolution variable severity. Further revealed that major affected groups shifted older individuals, who had higher age-specific CFRs. successive create challenges strategic preparedness health authorities make uncertain variable. Our findings indicate emergence new age shift high might contribute potentially occurrence severe offer insights into adjustment national responses mitigate pandemics.