Influenza virus characterisation, Summary Europe, July 2017
In the course of the 2016–17 influenza season, nearly 146 000 influenza detections have been reported across the WHO European Region. 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.)
Since 1 January 2017, EU/EEA countries have shared 592 influenza-positive specimens with collection dates after 31 December 2016. Since the June 2017 report 97 viruses have been characterised antigenically and 34 genetically. Many A(H3N2) viruses could only be characterised genetically as HA titres of these viruses were too low to allow antigenic characterisation by haemagglutination inhibition assay.
All nine 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. The subclade 6B.1 viruses, defined by HA1 amino acid substitutions S162N and I216T, became dominant worldwide and the 19 EU/EEA viruses characterised with 2017 collection dates were all within this subclade.
Fifty-seven A(H3N2) viruses had sufficient HA titre for characterisation by haemagglutination inhibition (HI) assay. Approximately half (25/57) were recognised well by antiserum raised against egg-propagated A/Hong Kong/4801/2014 (the current vaccine component). Of 147 A(H3N2) viruses characterised genetically with collection dates in 2017, 38 (26%) were subclade 3C.2a, 108 (73%) were subclade 3C.2a1, and one (1%) was 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. All 33 viruses characterised with collection dates in 2017, including viruses with the deletion in HA1, fell in genetic clade 1A, as do recently collected viruses worldwide.
Of the 18 B/Yamagata viruses characterised antigenically, 17 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 and for quadrivalent vaccines since 2016. Of the 65 viruses characterised with 2017 collection dates, all fell in genetic clade 3.
Influenza virus characterisation, December 2019
16 Jan 2020 - This is the third report for the 2019–20 influenza season. As of week 1/2020, 42 844 influenza detections had been reported across the WHO European Region; 85% type A viruses, with A(H3N2) prevailing over A(H1N1)pdm09, and 15% type B viruses, with 531 (92%) of 576 ascribed to a B/Victoria lineage.
Influenza virus characterisation, November 2019
11 Dec 2019 - This is the second influenza characterisation report for the 2019–20 influenza season. As of week 48/2019, 6 887 influenza detections across the WHO European Region had been reported; of which 84% were type A viruses, with A(H3N2) prevailing over A(H1N1)pdm09, and 16% type B viruses, with 123 of 137 (90%) ascribed to a lineage B/Victoria.
Influenza virus characterisation, October 2019
11 Nov 2019 - This is the first report for the 2019–20 influenza season. As of week 44/2019, 1 138 influenza detections across the WHO European Region had been reported; 80% type A viruses, with A(H3N2) prevailing over A(H1N1)pdm09, and 20% type B viruses, with 26 of 27 (96%) ascribed to a lineage being B/Victoria.