Influenza Virus Characterisation, Summary Europe, March 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, 23 EU/EEA countries have shared 650 influenza-positive specimens with the WHO Collaborating Centre in London for detailed characterisation. Since the February 2015 report1, 101 viruses have been characterised antigenically and 100 genetically.
Executive Summary
The 33 A(H1N1)pdm09 viruses characterised antigenically were similar to the vaccine virus A/California/07/2009, and all those characterised genetically had HA genes belonging to genetic subgroup 6B, as observed worldwide.
Many of the 36 A(H3N2) viruses characterised by haemagglutination inhibition (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. The 208 viruses, with collection dates after 31 August 2014, characterised genetically this season fell in genetic group/subgroups 3C.3 (19), 3C.3b (52), 3C.3a (19) and 3C.2a (118). 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.
No B/Victoria-lineage viruses were received since the February 2015 report.
The 32 characterised B/Yamagata-lineage test viruses fell in genetic clade 3 and showed good reactivity with antisera raised against B/Phuket/3073/2013 (the clade 3 virus recommended for the southern hemisphere 2015 and northern hemisphere 2015–16 vaccines). Antisera raised against B/Massachusetts/02/2012 (the clade 2 virus recommended for the 2014–15 northern hemisphere season vaccine) did not recognise test viruses as well as antisera raised against B/Phuket/3073/2013. However, the observed titres for the test viruses were similar with antisera raised against both vaccine viruses.
