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Proportions of circulating B/Yamagata strain isolates antigenically similar to egg- and MDCK cell-propagated reference viruses, as assessed by haemagglutination inhibition (HI) assay. Antigenic similarity is defined as circulating virus titre no more than 4-fold lower than reference virus titre. Data are displayed as percentage of the total number of isolates tested. Studied period September 2008 to September 2018.
