Influenza virus characterisation - Summary Europe, July 2020

This is the ninth report for the 2019-20 influenza season. As of week 30/2020, 164 887 influenza detections had been reported across the WHO European Region; 73% type A viruses, with A(H1N1)pdm09 prevailing over A(H3N2), and 27% type B viruses, with 4 479 (98%) of 4 568 ascribed to a B/Victoria lineage.

Since the June 2020 characterisation report report, three shipments of influenza positive specimens from EU/EEA countries have been received at the London WHO Collaborating Centre, the Francis Crick Worldwide Influenza Centre (WIC). In total (since wee k 40/2019) 2019), 1 661 virus specimens have been received, with collection dates after 31 August 2019.

Of the 4 9 A(H1N1)pdm09 viruses from EU/EEA countries characterised antigenically since the June report, 36 were well recognised by antisera raised against the 2019 20 vaccine virus, A/Brisbane/02/2018. The 13 viruses showing poor reactivity generally carried amino acid substitutions (notably N156K) in the HA1 150 loop region. The 468 EU/EEA test viruses with collec tion dates from week 40/2019 genetically characterised at the WIC have fallen within subclades of clade 6B.1A: 425 6B.1A5A, 30 6B.1A5B, 1 6B.1A6 and 12 6B.1A7.

The majority (39) of the 68 A(H3N2) viruses from EU/EEA countries characterised antigenically in July were clade 3C.3a and were well recognised by antiserum raised against egg propagated A/Kansas/14/2017, the current vaccine virus. Globally approximately equal proportions of clade 3C.3a and subgroups 3C.2a1b+T131K and 3C.2a1b+T135K viruses have bee n detected , but for viruses detected since 1 February 2020, subgroups 3c.2a1b+T135KA/B have prevailed in the USA while those of clade 3C.3a and subgroup 3C.2a1b+T131K have dominate d in Europe. In total, 500 viruses from EU/EEA countries have been characterised genetically at the WIC: 2 82 were clade 3C.3a, 1 37 were 3C.2a1b+T131K, 61 were 3C.2a1b+T135K A and 20 were 3C.2a1b+T135K B.

Thirty two B/Victoria lineage viruses from EU/EEA countries were antigenically characterised in July, all were subclade 1A(Δ3)B. Four viruses were not recognised well by antiserum raised against B/Washington/02/2019, the vaccine virus for the 2020 2021 northern hemisphere influenza season. Poor recognition was associated with HA1 a mino acid substitutions of either N126K or T155A . In total, 306 EU/EEA viruses have been characterised genetically at the WIC: 2 90 were sub clade 1A(Δ3)B and 1 6 were subclade 1A(Δ2).

A single B/Yamagata lineage virus from France, with a collection date in February 2020, was antigenically characterised in July. As for all recently circulating B/Yamagata lineage viruses a ll eight EU/EEA viruses characterised genetically at the WIC since week 40/2019 belong to genetic clade 3 and contain at least two HA amino acid substitutions (HA1 L172Q and M251V) compared to B/Phuket/3073/2013, the antigenic effects of which have been minimal as assessed in earlier reports.