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​WHO recommendations for influenza virus vaccine composition for the 2017-18 northern hemisphere season

16 Mar 2017
World Health Organization, Geneva, Switzerland – 2 March 2017, report published here
The World Health Organization (WHO) has agreed on the recommended composition of the trivalent influenza vaccine for the northern hemisphere winter 2017-18 influenza season as:
  • an A/Michigan/45/2015 (H1N1)pdm09-like virus;
  • an A/Hong Kong/4801/2014 (H3N2)-like virus; and
  • a B/Brisbane/60/2008-like virus (Victoria lineage).
For quadrivalent vaccines containing two influenza B viruses, the above three viruses and a B/Phuket/3073/2013-like virus (Yamagata lineage) should be included.
All four components of the vaccine recommended for the northern hemisphere remained the same as for the southern hemisphere 2017 season. Further antigenic and genetic characteristics of recent seasonal influenza viruses are described below and in the full report of the recommendation [1].
Influenza A(H1N1)pdm09 viruses
The genotyped influenza A(H1N1)pdm09 viruses circulating globally from September 2016 to February 2017 mainly fell into the phylogenetic clade 6B with the more recently circulating viruses belonging to the genetic subclade 6B.1. A small proportion of the genotyped viruses belonged to subclade 6B.2 with detections mostly in Asia and Oceania. Almost all recent influenza A(H1N1)pdm09 viruses were antigenically indistinguishable with ferret antisera from the vaccine viruses used since 2009: A/California/7/2009 and A/Michigan/45/2015 which are antigenically similar.
Influenza A(H3N2) viruses
The influenza A(H3N2) viruses circulating during the 2016-17 season fell genetically into phylogenetic clades 3C.2a and subclade 3C.2a1 and considerable diversification of the HA clades and subclades was evident. Antigenic characterisation of 3C.2a viruses continued to be technically difficult. Most recent A(H3N2) 3C.2a viruses were well inhibited by ferret antisera raised against cell culture-propagated reference viruses in clade 3C.2a, including A/Hong Kong/4801/2014. These antisera also inhibited well the majority of viruses in subclade 3C.2a1.
Influenza B viruses
The influenza B/Yamagata/16/88 and B/Victoria/2/87 lineage viruses have continued to co-circulate across the world. The majority of viruses of the B/Victoria-lineage are antigenically closely related to the earlier vaccine virus B/Brisbane/60/2008 and thus no change to the recommendation was issued and this remains the B virus recommended for use in trivalent vaccines. The majority of viruses of the B/Yamagata lineage are antigenically closely related to the virus currently included in as the fourth component in quadrivalent vaccines, B/Phuket/3073/2013, and therefore also no change of this recommendation was made. 

ECDC comment:
The WHO recommendations are made with a knowledge of the currently circulating viruses in Europe and globally. No changes to the components previously recommended for the southern hemisphere 2017 vaccine were recommended. The A(H1N1)pdm09 component was changed in the vaccine for the southern hemisphere after the 2015-16 northern hemisphere season from A/California/7/2009 to A/Michigan/45/2015.
Published interim results for the ongoing 2016 -17 northern hemisphere influenza season suggest moderate to low vaccine effectiveness against the recently circulating A(H3N2) viruses [2-5].  Challenges in egg-propagation of the A(H3N2) viruses used currently in the vaccines may explain the discrepancy between the antigenic characterisation and vaccine effectiveness results. In addition, technical difficulties in performing the haemagglutination inhibition test on these viruses continued. In the northern hemisphere, for the ongoing winter season the vaccine component for A(H1N1)pdm09 is still A/California/7/2009-like virus. The A/Michigan/45/2015-like viruses selected for the 2017-18 season are antigenically indistinguishable from A/California/7/2009 [1].
In Europe, both B virus lineages co-circulate with roughly equal proportions and it is impossible to forecast which lineage (if either) will predominate during the 2017 -18 season [6]. WHO recommended inclusion of the B/Victoria lineage into the trivalent vaccine, which is the most widely used vaccine in EU Member States.
As influenza A(H1N1)pdm09 viruses circulate and A(H3N2) viruses continue to drift, it is also impossible to predict the proportions of circulating viruses next season and the expected protection by the recommended vaccine components. The technical difficulties in virus culture, characterisation and egg-propagation of influenza A(H3N2) viruses continue to make the selection of new vaccine components difficult.
1. World Health Organisation. Recommended composition of influenza virus vaccines for use in the 2017- 2018 northern hemisphere influenza season. 2017.
2. Castilla J, Navascues A, Casado I, Diaz-Gonzalez J, Perez-Garcia A, Fernandino L, et al. Combined effectiveness of prior and current season influenza vaccination in northern Spain: 2016/17 mid-season analysis. Euro surveillance : bulletin europeen sur les maladies transmissibles = European communicable disease bulletin. 2017 Feb 16;22(7).
3. Hergens MP, Baum U, Brytting M, Ikonen N, Haveri A, Wiman A, et al. Mid-season real-time estimates of seasonal influenza vaccine effectiveness in persons 65 years and older in register-based surveillance, Stockholm County, Sweden, and Finland, January 2017. Euro surveillance : bulletin europeen sur les maladies transmissibles = European communicable disease bulletin. 2017 Feb 23;22(8).
4. Kissling E, Rondy M. Early 2016/17 vaccine effectiveness estimates against influenza A(H3N2): I-MOVE multicentre case control studies at primary care and hospital levels in Europe. Euro surveillance : bulletin europeen sur les maladies transmissibles = European communicable disease bulletin. 2017 Feb 16;22(7).
5. Skowronski DM, Chambers C, Sabaiduc S, Dickinson JA, Winter AL, De Serres G, et al. Interim estimates of 2016/17 vaccine effectiveness against influenza A(H3N2), Canada, January 2017. Euro surveillance : bulletin europeen sur les maladies transmissibles = European communicable disease bulletin. 2017 Feb 09;22(6).
6. European Centre for Disease Prevention and Control/ WHO Regional Office for Europe. Joint ECDC-WHO weekly influenza update 2017 [16 March 2017]. Available from:
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