Objectives: To study the resurgence of influenza B/Yam in Taiwan and summarize clinical findings of influenza B-associated complications among hospitalized patients, in particular the link between clinical and molecular epidemiologic characteristics. Methods: Clinical information and isolates were collected through the national surveillance system of the Taiwan Centers for Disease Control. Potential risk factors associated with severe illness were analyzed. Antigenic and genetic analysis of

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... esentative hemagglutinin (HA) nucleotide sequences was performed. Results: Of 326 patients admitted to the intensive care unit (ICU), 63.2% were aged 18 years or !65 years and 12.9% were adults aged 19-49 years. Most of the cases had underlying medical conditions before admission, and more fatal cases had chronic medical conditions than those who convalesced in the ICU. Results of the phylogenetic analysis showed that the majority of isolates from fatal cases in Taiwan were in group 2 (represented by B/Massachusetts/2/2012-like) rather than group 3, which was the predominant group of strains circulating in other Asian countries. Conclusions: Our findings suggest a regional trend of influenza B viruses and showed that new phylogenetic lineages and antigenic variants emerging in neighboring countries were likely to be the progenitors of the epidemic strains in the following seasons.