Genetic Characterisation of Influenza 2012/2013 Season

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Influenza B viruses have dominated the influenza 2012/2013 season in Ireland, although influenza A(H3N2) and A(H1N1)pdm09 have also been circulating.  Both B/Yamagata and B/Victoria lineages have been co-circulating, with the majority of influenza B viruses characterised as B/Yamagata. 

Since week 40 of the 2012/2013 influenza season, the National Virus Reference Laboratory has genetically characterised a selection of influenza positive specimens.  Of the influenza B viruses analysed, 87.5% (n=21) belong to the B-Yamagata lineage and 12.5% (n=3) to the B-Victoria lineage.  Of the B-Yamagata viruses, the majority (81%; n=17) belong to genetic clade 2 and are related to B/Estonia/55669/2011 and 19% (n=4) belong to genetic clade 3 and are related to the influenza B vaccine strain, B/Wisconsin/01/2010.  

Seven influenza A(H3N2) viruses were characterised and clustered with genetic group 3c of the A/Victoria/208/2009 clade and were similar to  the vaccine strain A/Victoria/361/2011. Sequence analysis of one influenza A(H1N1)pdm09 virus identified it was related to the vaccine strain A/California/07/2009 and clustered with genetic group 6 viruses similar to A/St.Petersburg/27/2011.