?Influenza virus characterisation, Summary Europe, February 2016
11 Mar 2016
From week 40/2015, the start of weekly reporting on influenza activity in the WHO European Region, to week 07/2016 over 70 000 influenza detections across the Region have been reported. Influenza type A viruses are prevailing over type B but, unlike the situation in the 2014–15 season, A(H1N1)pdm09 viruses are prevailing over A(H3N2), and the proportion of B/Victoria-lineage detections has risen substantially, representing ~92% of those ascribed to a B virus lineage.
To date, 23 EU/EEA countries have shared 424 influenza-positive specimens with the Francis Crick Institute, London, for detailed characterisation: 16 additional countries and 330 specimens since the December 2015 report. Since the latter report, 230 viruses have been characterised antigenically and genetic analyses are ongoing.
The 166 A(H1N1)pdm09 viruses characterised antigenically were similar to the vaccine virus A/California/7/2009. Worldwide new genetic sub-clusters of viruses within the 6B clade have emerged, with two being designated as subclades: 6B.1 defined by HA1 amino acid substitutions S162N and I216T and 6B.2 defined by HA1 amino acid substitutions V152T and V173I. Of the 123 viruses characterised genetically, 18 (14%) were clade 6B, 98 (80%) were subclade 6B.1 and seven (6%) were subclade 6B.2.
The 26 A(H3N2) test viruses characterised by haemagglutination inhibition (HI) assay were poorly recognised by reference antiserum raised against egg-propagated A/Switzerland/9715293/2013, the vaccine virus recommended for use in the 2015–2016 northern hemisphere influenza season, despite over 75% of the test viruses falling in the same genetic subclade (3C.3a) as the vaccine virus. The test viruses were recognised somewhat better by antisera raised against egg-propagated A/Hong Kong/4801/2014, the virus recommended for use in 2016 southern hemisphere and 2016–2017 northern hemisphere influenza vaccines. Of 40 A(H3N2) viruses characterised genetically: one (2%) was clade 3C.3, 23 (58%) were subclade 3C.2a and 16 (40%) were subclade 3C.3a.
The 33 B/Victoria-lineage viruses were antigenically similar to B/Brisbane/60/2008 and fell in genetic clade 1A as do recently collected viruses worldwide.
The five B/Yamagata viruses characterised fell in genetic clade 3 and 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 use in quadrivalent vaccines in the 2016 southern hemisphere and 2016–17 northern hemisphere influenza seasons.
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