Week 6/2018 (5-11 February 2018)

    • Influenza activity was widespread in the majority of reporting countries.
    • Both influenza virus types A and B were co-circulating with a higher proportion of type B viruses. Different proportions of circulating influenza virus types and A subtypes were observed between countries.
    • Of the individuals sampled, on presenting with ILI or ARI to sentinel primary healthcare sites, 51% tested positive for influenza viruses. The detection rate decreased compared to the previous week (55%).
    • The majority of severe cases reported this season are due to influenza B and occur in persons above the age of 15 years. In confirmed influenza cases in ICU, similar numbers of cases were infected with influenza A or influenza B. In laboratory confirmed cases reported in wards other than ICU, influenza B was detected approximately twice as frequently as influenza A and mainly in the >65 age group.
    • WHO is convening the Vaccine Composition Meeting on 19–21 February to decide on the composition of the 2018–2019 Northern hemisphere vaccine.

 

2017/18 season overview 

  • For the Region overall, a higher proportion of type B compared to type A viruses has been detected in sentinel and non-sentinel sources. Of the type A detections from sentinel sources, A(H1N1)pdm09 viruses have outnumbered A(H3N2) viruses, while in non-sentinel sources more A(H3N2) viruses were reported than A(H1N1)pdm09 viruses.
  • The majority of severe cases reported this season are due to influenza B and occur in persons above the age of 15 years. In confirmed influenza cases in ICU, similar numbers of cases were infected with influenza A or influenza B and approximately equal numbers of cases were reported in the 15–64 and >64 age groups. In laboratory confirmed cases reported in wards other than ICU, influenza B was detected approximately twice as frequently as influenza A and twice as many cases occurred among those >64 compared with patients in the 15–64 age group.
  • For type B viruses from both sentinel and non-sentinel sources, B/Yamagata lineage viruses have greatly outnumbered those of the B/Victoria lineage. The current trivalent seasonal influenza vaccine does not include a virus from the B/Yamagata lineage.
  • Different patterns of dominant type and A subtype were observed between the countries in the Region, which may be due to differences in relative weights of information being derived from sentinel, non-sentinel and severe influenza case sources of information between countries.
  • While low in number, 59% of the genetically characterized A(H3N2) viruses belong to clade 3C.2a, the clade of the vaccine virus described in the WHO recommendations for vaccine composition for the northern hemisphere 2017–2018, and 37% to subclade 3C.2a1, with mammalian cell-cultured viruses in both clades being antigenically similar.
  • A situation analysis that describes the early season evolving epidemiological pattern was published by WHO Regional Office for Europe in January. A high level of influenza B virus circulation was observed during the first half of the season, compared to previous seasons.
  • An early risk assessment based on data from EU/EEA countries was published by ECDC on 20 December 2017.
  • Interim or real-time vaccine effectiveness estimates from Canada, Finland, Germany, Spain, Stockholm County and the United States of America suggest overall vaccine effectiveness of 15–46%, depending on the proportion of circulating (sub)types. Effectiveness against influenza B is in the range of 35–67%, despite the circulating lineage not being included in the more commonly used trivalent vaccine.
  • European mortality among the elderly has significantly increased over the past weeks in the western parts of Europe.
  • Additional information on global influenza activity is available from WHO’s biweekly global updates.

To display at the boottom of this page influenza detections by week and the pie chart with the detected subtypes, please choose the season 2017-2018 first and press update

Influenza intensity, spread and dominant virus type/subtype