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ECDC: Influenza virus characterisation, Summary Europe, February 2015

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  • ECDC: Influenza virus characterisation, Summary Europe, February 2015

    Over the course of the 2014?15 influenza season, influenza A(H3N2), A(H1N1)pdm09 and type B viruses have co-circulated in EU/EEA countries. To date, 21 EU/EEA countries have shared 545 influenza-positive specimens with the WHO Collaborating Centre in London for detailed characterisation. Since the December 2014 report1, 236 viruses have been characterised. The 71 A(H1N1)pdm09 viruses characterised, as those circulating worldwide, belonged to genetic subgroup 6B and were antigenically similar to the vaccine virus A/California/07/2009, based on HI analyses. Many of the 101 A(H3N2) viruses characterised by HI assay were poorly recognised by antisera raised against the A/Texas/50/2012 vaccine virus but relatively well recognised by antisera raised against cell-propagated genetic subgroup 3C.3a viruses, although the small number of genetic subgroup 3C.2a viruses that could be analysed by HI assay showed somewhat lower HI titres. The 85 viruses characterised genetically fell in genetic group/subgroups 3C.3 (17), 3C.3b (29), 3C.3a (15) and 3C.2a (24). Viruses in genetic group 3C.3 and subgroup 3C.3b were antigenically similar to A/Texas/50/2012, while those in subgroups 3C.2a and 3C.3a were antigenically distinct and the two subgroups were antigenically distinguishable despite antisera raised against representative viruses showing cross-reactivity. A subset of A(H3N2) viruses analysed by plaque reduction neutralisation assay (PRNA: n = 49, inclusive of many that could not be analysed by HI assay) also showed the cross-reactivity of antisera raised against genetic subgroup 3C.2a and 3C.3a viruses. Only two B/Victoria-lineage viruses were received. Both were antigenically and genetically similar to B/Brisbane/60/2008.

    full report: