Influenza virus characterisation, Summary Europe, September 2017
In the course of the 2016–17 influenza season, over 146 000 influenza detections across the WHO Europe Region have been reported. Influenza type A viruses have prevailed over type B with A(H3N2) viruses, greatly outnumbering A(H1N1)pdm09 and B/Yamagata-lineage detections (representing 73% of the type B viruses assigned to a lineage).
Executive Summary
Since 1 February 2017, EU/EEA countries have shared 304 influenza positive specimens with collection dates after 31 January 2017. Since the July 2017 report, 52 viruses have been characterised antigenically and 287 genetically. The HA titres of many A(H3N2) viruses were so low that they could not be characterised antigenically by haemagglutination inhibition (HI) assay.
All seven A(H1N1)pdm09 viruses characterised antigenically were similar to the 2016–17 vaccine virus, A/California/7/2009, and showed good reactivity with antiserum raised against the subclade 6B.1 2017–18 vaccine virus, A/Michigan/45/2015. Subclade 6B.1 viruses, defined by HA1 amino acid substitutions S162N and I216T, rapidly became dominant worldwide, and all (32) EU/EEA viruses with 2017 collection dates have fallen within this subclade.
Seventeen A(H3N2) viruses had sufficient HA titre for characterisation by HI assay. Over half (13/17) were recognised well by antiserum raised against egg-propagated A/Hong Kong/4801/2014 (the current vaccine component). Of 357 A(H3N2) viruses characterised genetically with collection dates in 2017, 124 (35%) were subclade 3C.2a, 228 (64%) were subclade 3C.2a1, and five (1%) were subclade 3C.3a.
Of the 13 B/Victoria-lineage viruses tested, all were antigenically similar to tissue culture-propagated surrogates of B/Brisbane/60/2008 (current vaccine component for the northern hemisphere 2017–18 season). All 55 viruses characterised with collection dates in 2017, including viruses with deletion in HA1, fell in genetic clade 1A, as do recently collected viruses worldwide.
Of the 15 B/Yamagata viruses characterised antigenically, 14 reacted well with post-infection ferret antiserum raised against egg-propagated B/Phuket/3073/2013, the recommended vaccine virus for the northern hemisphere 2015–16 influenza season, for quadrivalent vaccines since 2016 and for trivalent vaccines in the southern hemisphere 2018 season. Of the 89 viruses characterised with 2017 collection dates, all fell in genetic clade 3.
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