Virus characteristics


Genetic characterization

For specimens collected since week 40/2016, genetic characterizations of 1 649 viruses have been reported (Table 3).

Among 1 502 A(H3N2) viruses, 423 fell in the vaccine component clade (3C.2a), and 1 056 in a subclade of clade 3C.2a viruses (3C.2a1) defined by N171K, often with N121K, amino acid substitutions in the haemagglutinin. Viruses in these two clades are antigenically similar, though the 3C.2a1 subclade is evolving rapidly with emergence of numerous virus clusters defined by additional amino acid substitutions in haemagglutinin, the impact of which on antigenic characteristics is not yet clear.

 Table. Viruses attributed to genetic groups, cumulative for weeks 40/2016–5/2017


Phylogenetic group

Number of viruses

A(H1N1)pdm09 A/Michigan/45/2015 (subgroup 6B.1)b


A(H1N1)pdm09 A/South Africa/3626/2013 (subgroup 6B)a


A(H3N2) A/Bolzano/7/2016 (subgroup 3C.2a1)a, b



A(H3N2) A/Hong Kong/4801/2014 (subgroup3C.2a)a


A(H3N2) A/Switzerland/9715293/2013 subgroup (3C.3a)a


A(H3N2), subgroup not listed


B/Brisbane/60/2008 (Victoria lineage clade 1A)a, b


B (Victoria lineage), not attributed to clade


B/Phuket/3073/2013 (Yamagata lineage clade 3)c


B (Yamagata lineage), not attributed to clade


a Vaccine component for Northern Hemisphere 2016–2017 season

b Vaccine component for Southern Hemisphere 2017 season

c Vaccine component of quadrivalent vaccines for use in both season 


The recommended composition of trivalent influenza vaccines for the 2016–2017 season in the northern hemisphere is for inclusion of an A/California/7/2009 (H1N1)pdm09-like virus; an A/Hong Kong/4801/2014 (H3N2)-like virus; and a B/Brisbane/60/2008-like virus (B/Victoria lineage). For quadrivalent vaccines a B/Phuket/3073/2013-like virus (B/Yamagata lineage) virus is recommended. The recommended influenza A(H1N1)pdm09 component of the 2017 southern hemisphere influenza vaccine is an A/Michigan/48/2015 (H1N1)pdm09-like virus, the first update since A(H1N1)pdm09 viruses emerged in 2009.

Early monitoring of vaccine effectiveness in Finland and Sweden suggested levels of effectiveness in persons aged 65 years or older (26%) and 24% vaccine effectiveness, respectively) similar to estimates from annual multi-country studies covering the 2011–2012 and 2014–2015 seasons. More recent VE 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.

Antiviral susceptibility testing

Neuraminidase inhibitor susceptibility has been assessed for 918 viruses (867 A(H3N2), 12 A(H1N1)pdm09 and 39 type B with collection dates since week 40/2016. None showed evidence of reduced inhibition to oseltamivir or zanamivir.

Viruses detected from non-sentinel sources 

For week 6/2017, 6 327 specimens from non-sentinel sources (such as hospitals, schools, non-sentinel primary care facilities, nursing homes and other institutions) tested positive for influenza viruses (Table 2). Of these, 88% were type A (with 99% of the subtyped viruses being A(H3N2)), and 12% type B.

Similar cumulative distributions of types and subtypes as seen in sentinel detections have been observed since week 40/2016 with A(H3N2) viruses being dominant throughout Europe (Table 2).

For the majority of viruses no subtype or lineage was determined. However, for those that were, 99% of the subtyped influenza A viruses were A(H3N2), while of 490 type B viruses ascribed to a lineage, 64% were B/Yamagata lineage and 36% were B/Victoria lineage.

Figure. Influenza virus detections in non-sentinel-source specimens by type and subtype, by week