Week 6/2017 (6-12 February 2017)

  • Influenza activity remained elevated across the region with 24 of 43 countries reporting medium to very high intensity and 22 reporting widespread influenza activity.
  • The proportion of influenza virus detections among sentinel surveillance specimens decreased slightly to 42% from 45% in the previous week.
  • The great majority of influenza viruses detected were type A (92%) and, of those subtyped, 99% were A(H3N2).
  • The number of new hospitalized laboratory-confirmed influenza cases reported, primarily in people aged 65 years or older, continued to decrease.

Season overview

  • Influenza activity started early in week 46/2016, which is the earliest week that the overall influenza-positivity rate in sentinel specimens reached 10% since the emergence of A(H1N1)pdm09 viruses in 2009/10.
  • Since week 40/2016, influenza A viruses have predominated, accounting for 96% of all sentinel detections; the great majority (99%) of subtyped influenza A viruses from sentinel sites being A(H3N2).
  • Confirmed cases of influenza virus type A infection reported from hospitals have predominantly been in adults aged over 65 years. Excess all-cause mortality has been observed substantially in people aged 15–64 years and markedly in people aged 65 years or older in the majority of the 19 reporting countries. This is commonly seen when the predominant viruses circulating are A(H3N2).
  • Two-thirds of the A(H3N2) viruses genetically characterized belong to a recently emerged genetic subclade (3C.2a1). However, those that have been antigenically characterized are similar to the clade 3C.2a vaccine virus.
  • Recent vaccine effectiveness estimates, for all age groups against A(H3N2) illness, from Canada (42%), from the US (43%) and from Europe (38%) are consistent with estimates from Sweden and Finland early in the season.
  • Given typically suboptimal vaccination coverage and the partial effectiveness of influenza vaccines, rapid use of neuraminidase inhibitors (NAIs) for laboratory-confirmed or probable cases of influenza infection should be considered for vaccinated and non-vaccinated patients at risk of developing complications.
  • No reduced susceptibility to oseltamivir or zanamivir has been observed for any of the 918 viruses tested so far this season.
  • The progression of the season thus far has confirmed the conclusions of the ECDC risk assessment on seasonal influenza updated on 25 January 2017, namely expected severe outcomes in the elderly related to the large circulation of A(H3N2) putting some health care systems under pressure.

 

 

Influenza intensity, spread and dominant virus type/subtype