Influenza virus characterisation, summary Europe, August and September 2011

Influenza A(H1N1)pdm09, influenza A(H3N2), and influenza B/Victoria- and B/Yamagata-lineage viruses have been characterised genetically and antigenically.• A(H1N1)pdm09 viruses collected since 1 February 2011 fall into several genetic groups but all groups show antigenic similarity to the currently recommended vaccine virus A/California/7/2009.• A(H3N2) viruses collected since 1 February 2011 fall into distinct genetic groups. There is no consistent correlation of altered antigenicity compared to the vaccine virus, A/Perth/16/2009, with any genetic group.• Influenza B viruses of the B/Victoria/2/87 lineage have predominated over those of the B/Yamagata/16/88 lineage. Most of the B/Victoria/2/87 lineage viruses remain genetically similar to the currently recommended vaccine virus B/Brisbane/60/2008 and antigenically similar to cell-propagated viruses that are genetically closely related to the vaccine virus B/Brisbane/60/2008.• The majority of influenza B viruses of the B/Yamagata-lineage are in the B/Bangladesh/3333/2007 genetic clade.