Virus characteristics

 

Viruses detected from non-sentinel sources 

For weeks 30–34/2017, 5 593 specimens from non-sentinel sources were tested (such as hospitals, schools, non-sentinel primary care facilities, nursing homes and other institutions), of which 109 were positive for influenza viruses. Of the 109 detections, 74% were type A (85% of all subtyped viruses being A(H3N2)) and 26% type B.

Table. Influenza viruses detected in non-sentinel-source specimens, by virus (sub)type,  cumulatively for weeks 30-34/2017

Virus type and subtype

Weeks 30-34/2017

Number

%a

Influenza A

 81

74

A(H1N1)pdm09

 7

15

A(H3N2)

 39

85

A not subtyped

 35

-

Influenza B

 28

26

B/Victoria lineage

 0

0

B/Yamagata lineage

 2

100

Unknown lineage

 26

-

Total detections / Total tested

109/5 593

2


 a
For influenza type percentage calculations, the denominator is total detections; for subtype and lineage, it is total influenza A subtyped and total influenza B lineage determined, respectively; as not all countries have a true non-sentinel testing denominator, no percentage calculations for total tested are shown.

 

 

Genetic characterization

Since week 21/2017, genetic characterization of 5 viruses has been reported. Of these, 3 were B/Yamagata lineage viruses (clade 3), 1 A(H3N2) fell into the 3C.2a1 subclade defined by N171K amino acid substitution, often with N121K, in the haemagglutinin. Viruses in this clade have been antigenically similar to the vaccine component clade (3C.2a), but both clades are evolving rapidly with the emergence of several virus clusters defined by additional amino acid substitutions in the haemagglutinin, thereby requiring continued monitoring of antigenic characteristics. Additionally, 1 A(H1N1)pdm09 virus was genetically characterised and fell in the sub-group 6B.1. See also the ECDC summary report for June.

The recommended composition of trivalent influenza vaccines for the 2016–2017 season in the northern hemisphere was 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) was recommended. On 2 March 2017, WHO announced the recommended vaccine composition for the 2017–2018 season in the northern hemisphere. The recommendations matched those for the 2017 southern hemisphere season, with a changed A(H1N1)pdm09 component to an A/Michigan/48/2015-like virus (clade 6B.1).

Overall vaccine effectiveness of influenza vaccines for the 2016–2017 season was estimated at 44% in European primary care settings (I-MOVE) and 49% in the United States of America (CDC).

Antiviral susceptibility testing

No viruses with collection dates from week 30/2017 through week 34/2017 have been tested for antiviral susceptibility.