Week 1/2017 (2 - 8 January 2017)
- Influenza activity remained high across the region with high or very high intensity in 10 out of 43 reporting countries.
- The proportion of influenza virus detections among sentinel surveillance specimens was around 50% for the third consecutive week.
- The great majority of influenza viruses detected were type A and, of those subtyped, 99% were A(H3N2).
- The number of influenza cases from hospital settings also increased, markedly for predominantly adults aged over 65 diagnosed with influenza A virus infection.
- Excess all-cause mortality seems to have been increasing among the elderly, notably in France and Portugal (EuroMOMO).
- Influenza activity started early this season compared to previous seasons.
- Week 46/2016 is the earliest week that the overall influenza-positivity rate in sentinel specimens reached 10% since the emergence of A(H1N1)pdm09 viruses in the 2009 season; during the last 6 seasons this occurred between weeks 48 and 51.
- 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 has been A(H3N2). This is in contrast to the same period during the 2015-16 season in which influenza A(H1N1)pdm09 viruses predominated, but similar to the 2014-15 influenza season, when influenza A(H3N2) was predominant.
- In an influenza season in which A(H3N2) viruses predominate, elderly populations can be expected to be most severely affected.
- So far, circulating A(H3N2) viruses are antigenically similar to the vaccine strain. While about two-thirds of the A(H3N2) viruses characterized belong to a new genetic subclade (3C.2a1), these viruses are antigenically similar to the vaccine strain (clade 3C.2a).
- Early monitoring of vaccine effectiveness in Finland and Sweden suggests levels of effectiveness within estimates from multi-country studies during the seasons 2011-12 to 2014-15 with a 26% (95%CI 22%–30%) and 24% (95%CI 11%–34%) vaccine effectiveness in persons aged 65 years and older with laboratory-confirmed influenza A, respectively. Given the partial effectiveness of influenza vaccines, rapid use of neuraminidase inhibitors for laboratory-confirmed or probable cases of influenza should be considered for vaccinated and non-vaccinated patients at risk of complications following an influenza virus infection.
- A risk assessment on seasonal influenza in EU/EEA countries was published by ECDC on 24 December 2016. The above summary is in line with the findings of the risk assessment.
Figure. Influenza virus detections in sentinel-source specimens by type and subtype, by week and cumulatively