Influenza virus characterisation, Summary Europe, November 2017
This is the first report for the 2017–18 influenza season. As of week 48/2017 nearly 3 000 influenza detections have been reported across the WHO European Region. Co-circulating type A viruses are prevalent over type B, with A(H3N2) less prevalent than A(H1N1)pdm09 viruses and B/Yamagata more prevalent than B/Victoria viruses.
Only two EU/EEA countries have shared influenza positive specimens with the London WHO CC since week 40/2017. Of the 31 specimens received, 23 have collection dates after 31 August 2017 which fall within the time period (1 September 2017 to 31 January 2018) to be considered for the February 2018 WHO Vaccine Consultation Meeting (VCM).
The four A(H1N1)pdm09 viruses characterised antigenically showed good reactivity with antiserum raised against the 2017–18 vaccine virus, A/Michigan/45/2015. While genetic analysis of three viruses is pending, one virus - and others from the European region with collection dates after 31 August 2017 deposited in GISAID - have all fallen in subclade 6B.1, defined by HA1 amino acid substitutions S162N and I216T, many with additional substitutions of S74R, S164T and I295V.
None of the 13 A(H3N2) viruses recovered to date had sufficient HA titre to allow antigenic characterisation by HI assay in the presence of oseltamivir. While genetic analysis of these viruses is pending others - from the European region with collection dates after 31 August 2017 deposited in GISAID - fall within the 3C.2a genetic clade, with a minority falling in the 3C.2a1 genetic subclade.
The two B/Victoria-lineage viruses tested, both from Norway, have collection dates in June 2017 and both were antigenically distinct from tissue culture-propagated surrogates of B/Brisbane/60/2008. Phylogenetic analyses showed both viruses to carry an HA1 double amino acid deletion, falling within a subcluster of genetic clade 1A viruses with recently circulating viruses from Canada, Trinidad and the USA.
Of the five B/Yamagata viruses characterised antigenically, four reacted well with post-infection ferret antiserum raised against egg-propagated B/Phuket/3073/2013, the recommended vaccine virus for use in quadrivalent vaccines for 2017–18 and for trivalent vaccines in the southern hemisphere 2018 season. The two characterised viruses, like others recently circulating in the European region and reported to GISAID, fall within genetic clade 3.
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