Driffed Influenza A(H3N2) Viruses Circulate As
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Rapid communications Start of the 2014/15 influenza season in Europe: drifted influenza A(H3N2) viruses circulate as dominant subtype E Broberg ([email protected])1, R Snacken1, C Adlhoch1, J Beauté1, M Galinska2, D Pereyaslov2, C Brown2, P Penttinen1, on behalf of the WHO European Region and the European Influenza Surveillance Network3 1. European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden 2. World Health Organization (WHO) Regional Office for Europe, Copenhagen, Denmark 3. The members of the network are listed at the end of the article Citation style for this article: Broberg E, Snacken R, Adlhoch C, Beauté J, Galinska M, Pereyaslov D, Brown C, Penttinen P, on behalf of the WHO European Region and the European Influenza Surveillance Network. Start of the 2014/15 influenza season in Europe: drifted influenza A(H3N2) viruses circulate as dominant subtype. Euro Surveill. 2015;20(4):pii=21023. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=21023 Article submitted on 22 January 2015 / published on 29 January 2015 The influenza season 2014/15 started in Europe in influenza (timing and spread), its impact and sever- week 50 2014 with influenza A(H3N2) viruses predomi- ity (groups which are most affected), the predominat- nating. The majority of the A(H3N2) viruses character- ing influenza type and subtype, as well as analyses of ised antigenically and/or genetically differ from the virus strains to support the WHO recommendations for northern hemisphere vaccine component which may the composition of seasonal influenza vaccines (www. result in reduced vaccine effectiveness for the season. flunewseurope.org). The northern hemisphere influ- We therefore anticipate that this season may be more enza vaccine composition recommendation is given by severe than the 2013/14 season. Treating influenza WHO at the end of February each year. with antivirals in addition to prevention with vaccina- tion will be important. Influenza surveillance in Europe is mainly based on primary care sentinel sites collecting specimens from Influenza activity started increasing in the west- patients with ILI and/or ARI [1,3]. Data are collected ern part of the World Health Organization (WHO) at the national level and reported to the European European Region during week 50 2014, when Malta, level according to standardised case definitions [4,5]. the Netherlands and Sweden reported medium inten- The national influenza centres perform antigenic and sity of influenza activity which refers to usual activ- genetic characterisation of influenza viruses as well as ity of influenza season [1]. Rates of influenza-like antiviral susceptibility testing of a representative sam- illness (ILI) and/or acute respiratory infection (ARI) ple of virus isolates. have continued to increase, and in week 2 2015, 13 countries (Albania, Finland, France, Greece, Iceland, In addition to the primary care surveillance, particu- Malta, the Netherlands, Portugal, Slovenia, Spain, larly since the 2009 influenza A(H1N1) pandemic, hos- Sweden, Switzerland, the United Kingdom (UK)) in pital surveillance of laboratory-confirmed influenza the WHO European Region reported medium intensity cases has been conducted, including for this season, and Albania, the Netherlands, Portugal, Spain and in Finland, France, Ireland, Spain, Sweden and the UK. Switzerland had ILI rates above the epidemic thresh- Additionally, sentinel severe acute respiratory infec- old for the pre-season [2]. Of the 13 countries report- tion (SARI) surveillance is in place in 13 countries [1]. ing medium intensity, six (Finland, the Netherlands, Portugal, Slovenia, Sweden and the UK (England)) Virological situation in primary healthcare reported patterns of widespread activity with labora- The overall proportion of influenza-positive sentinel tory-confirmed influenza cases in 50% or more of their specimens increased from 4% to 39% from week 47 administrative units (or reporting sites). 2014 to week 2 2015, indicating the start of the sea- son at a similar time to the previous season (Figure 1). Influenza surveillance in Europe The season threshold of 10% was exceeded in season Since October 2014, all 53 Member States of the WHO 2011/12 and 2013/14 in week 51, in 2012/13 in week 49, European Region report their epidemiological and viro- and in the current season during week 50 (Figure 1). logical influenza surveillance data to The European Surveillance System (TESSy), hosted by the European In most countries, influenza A(H3N2) virus was the Centre for Disease Prevention and Control (ECDC) [1]. dominant subtype in both sentinel and non-sentinel The data are jointly published with the WHO European specimens in week 2 2015. In the sentinel systems, Regional Office to describe the annual occurrence of since week 40, 1,134 (10%) of the 11,854 specimens www.eurosurveillance.org 1 Figure 1 Number of influenza virus-positive sentinel specimens by (sub)type and week, and proportion of positive specimens compared to three previous seasons, World Health Organization European Region, weeks 40 2014–2 2015 for season 2014/15 500 Influenza B, 2014/15 70 Influenza A(H3N2), 2014/15 Influenza A(H1N1)pdm09, 2014/15 450 Influenza A not subtyped, 2014/15 Positive specimens (%), 2014/15 60 Positive specimens (%), 2011/12 400 s Positive specimens (%), 2012/13 n P e Positive specimens (%), 2013/14 roportion of m i Season threshold c 50 350 e p s l e n i t 300 p n os e 40 s i t e i v v i e t 250 i s s p o eci p f 30 o m r 200 en e b s m ( % u N 150 ) 20 100 10 50 0 0 40 41 42 43 44 45 46 47 48 49 50 51 52 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Week collected in 35 countries tested positive for influenza, containing antigenic drift variants compared with A/ 901 (79%) for type A influenza virus and 233 (21%) for Texas/50/2012, the vaccine component for the north- type B (Figure 1). Of the 831 type A viruses subtyped, ern hemisphere 2014/15 season [6]. 688 (83%) were A(H3N2) and 143 (17%) were A(H1N1) pdm09 by week 2 2015 (Figure 1). The lineage of 87 For 63 viruses, Norway, Spain and Sweden reported type B viruses was determined: six were B/Victoria lin- the haemagglutinin gene sequence accession num- eage and 81 B/Yamagata lineage. ber for the Global Initiative on Sharing All Influenza Data (GISAID) EpiFlu database. The maximum like- The antigenic characteristics of 117 influenza viruses lihood phylogenetic tree of these viruses together and the genetic characteristics of 202 influenza with the A(H3N2) reference viruses shows that the viruses were reported to TESSy by 16 countries mainly current circulating viruses cluster mainly with the in the western countries of the Region. Of 68 influenza genetic subgroups 3C.3, 3C.3a together with the A/ A(H3N2) viruses antigenically characterised, 40 were Switzerland/9715293/2013, and 3C.2a with the A/ reported by the national influenza centres as A(H3N2) Hong Kong/5738/2014, and show genetic drift from the A/Texas/50/2012-like (vaccine-like) and 26 were A/ current vaccine virus (Figure 2). The antigenic drift of Switzerland/9715293/2013-like (antigenically different viruses clustering with the A/Newcastle/22/2014 has from the vaccine); two viruses could not be ascribed not yet been shown. to an antigenic category. All 21 A(H1N1)pdm09 viruses characterised were A/California/7/2009-like (vaccine Ninety-three influenza A(H3N2) viruses, 20 A(H1N1) strain). Of the 30 influenza B viruses characterised, pdm09 and four influenza B viruses have been 28 were of the B/Yamagata/16/88-lineage (10 were tested phenotypically or genotypically for neuramini- reported as B/Massachusetts/02/2012-like viruses, one dase inhibitor susceptibility. None showed evidence B/Wisconsin/1/2010-like and 17 B/Phuket/3073/2013- of reduced susceptibility to either oseltamivir or like) and two were B/Brisbane/60/2008-like viruses of zanamivir. the Victoria lineage. Of the 160 genetically characterised A(H3N2) viruses, 110 (69%) fall in two genetic subgroups 2 www.eurosurveillance.org Figure 2 Laboratory-confirmed hospitalised Maximum likelihood phylogenetic tree of haemagglutinin influenza cases nucleotide sequences (1,063 nucleotides) from influenza Current surveillance systems reporting laboratory- A(H3N2) viruses reported to the European Surveillance System and reference A(H3N2) viruses, weeks 40 2014–1 confirmed hospitalised influenza cases to TESSy, while 2015 not being representative on a population basis in all A/Norway/3104/2014 EPI553159 countries, provide information on groups being hos- 63 A/Norway/3011/2014 EPI552640 A/Norway/3030/2014 EPI552641 pitalised due to influenza as well as risk factors for A/Malmoe/5/2014 EPI552706 A/Stockholm/28/2014 EPI552698 severe disease. This season, as of week 40 2014, six A/Newcastle/22/2014 EPI539874 countries with a monitoring system for laboratory-con- A/Norway/3041/2014 EPI552644 A/Norway/3101/2014 EPI553157 firmed hospitalised influenza cases reported 719 labo- A/Norway/3051/2014 EPI552647 96 83 A/Norway/3048/2014 EPI552646 ratory-confirmed hospitalised cases. In intensive care A/Lithuania/13347/2014 EPI539598 units (ICU), 671 cases were reported: three in Finland, A/Norway/3002/2014 EPI552638 A/Norway/3004/2014 EPI552639 101 in France, 20 in Spain, five in Sweden and 542 in A/LaRioja/2053/2014 EPI552658 89 65 the UK. In comparison, for season 2013/14, by week 2 A/LaRioja/2052/2014 EPI552657 71 A/LaRioja/2051/2014 EPI552656 2014, France had reported 77, Ireland two, Spain 227 A/LaRioja/2050/2014 EPI552655 A/Aragon/2062/2014 EPI553188 and Sweden 11 ICU cases. The UK had not reported a 68 A/Aragon/2031/2014 EPI552654 3C.3 single severe case by week 2 2014 and the surveillance A/Iceland/08202/2014 EPI536340 A/Galicia/1786/2014 EPI539568 system there has not changed.