WHO recommendations for influenza virus vaccine composition for the 2017 southern hemisphere season

ECDC comment

​The WHO recommendations are in line with the currently circulating viruses in the southern hemisphere, and the change of the influenza A(H1N1)pdm09 vaccine component is based on the available surveillance and virus characterisation data.

​World Health Organization, Geneva, Switzerland – 29 September 2016, report published here.

The World Health Organization (WHO) has agreed on the recommended composition of the trivalent influenza vaccine for the southern hemisphere winter 2016 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.

This is the first time that WHO has recommended a change of the A(H1N1)pdm09 component since the 2009 influenza A pandemic. The reason for the change is that the recently circulating A(H1N1)pdm09 viruses were distinguishable from the earlier vaccine strain A/California/7/2009 vaccine virus when tested with human post-vaccination sera. Two influenza A subtypes and two type B lineages have been circulating in the southern hemisphere in the 2016 influenza season with variable levels of activity. 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 February to August 2016 mainly fell into the phylogenetic clade 6B.1. A small proportion of the genotyped viruses belonged to subclade 6B.2 with detections mostly in China. Almost all recent influenza A(H1N1)pdm09 viruses were antigenically indistinguishable with ferret antisera from the earlier vaccine virus A/California/7/2009. However, representative 6B.1 and 6B.2 viruses were poorly inhibited by some post-vaccination adult human serum pools and therefore a new vaccine virus has been selected, represented by A/Michigan/45/2015 (H1N1)pdm09-like virus from the 6B.1 subclade.

Influenza A(H3N2) viruses

The most recently circulating influenza A(H3N2) viruses fell genetically into phylogenetic clades 3C.2 and 3C.3. Viruses in sub-clade 3C.2a predominated in all regions of the world and there is no change to the influenza A(H3N2) vaccine component which is represented by A/Hong Kong/4801/2014 (H3N2)-like virus from the 3C.2a subclade. The influenza A(H3N2) viruses continue to evolve with the majority of the 3C.2a viruses having further changes in the haemagglutinin (substitutions N171K, I406V and G484E), now referred to as subclade 3C.2a1. The most recent influenza A(H3N2) 3C.2a viruses were well inhibited by ferret antisera raised against current A/Hong Kong/4801/2014 vaccine virus. This antiserum also inhibited a majority of viruses in subclades 3C.2a1, 3C.3a and 3C.3b.

Influenza B viruses

The influenza B/Yamagata/16/88 and B/Victoria/2/87 lineage viruses have continued to co-circulate across the world with a predominance of the B/Victoria lineage in many countries. 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.

ECDC comment

The WHO recommendations are in line with the currently circulating viruses in the southern hemisphere, and the change of the influenza A(H1N1)pdm09 vaccine component is based on the available surveillance and virus characterisation data.

The influenza A(H1N1)pdm09 viruses continue to evolve and the 6B.1 subclade has become predominant. The new A/Michigan/45/2015 A(H1N1)pdm09 vaccine virus is closer to the circulating A(H1N1)pdm09 viruses in its genetic and antigenic properties than the earlier A/California/7/2009 vaccine component. Vaccine effectiveness against the earlier vaccine component in Europe in the 2015–2016 season was moderate [2] [3] [4]. In the northern hemisphere, for the upcoming winter season the vaccine component for A(H1N1)pdm09 is still A/California/7/2009-like virus [5].

Antigenic characterisation of influenza A(H3N2) subclade 3C.2a viruses continues to be technically challenging but most recent 3C.2a viruses were well inhibited by ferret antisera raised against the current northern hemisphere vaccine component. Influenza A(H3N2) viruses were circulating in low levels in the northern hemisphere in the 2015–2016 season with a majority of the viruses antigenically similar to the vaccine component [6]. However, there were too few detections to be able to estimate any vaccine effectiveness results in Europe.

In the northern hemisphere, both B virus lineages have co-circulated with the predominance of B/Victoria lineage viruses [6]. Vaccine effectiveness studies showed moderate effectiveness against B viruses in the 2015–2016 season if quadrivalent vaccine with both B virus components was used [2] [3]. Based on the higher prevalence of B/Victoria lineage viruses in the southern hemisphere 2016 season, it is expected that the Victoria-lineage prevalence will continue in the northern hemisphere over the 2016–2017 influenza season.

As both influenza A(H1N1)pdm09 and A(H3N2) viruses continue to drift, it is difficult to estimate with confidence 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 make the selection of new vaccine components difficult.

References

  1. World Health Organization. Recommended composition of influenza virus vaccines for use in the 2017 southern hemisphere influenza season2016 5 October 2016. Available from: http://www.who.int/influenza/vaccines/virus/recommendations/201609_recommendation.pdf.
  2. Pebody R, Warburton F, Ellis J, Andrews N, Potts A, Cottrell S, et al. Effectiveness of seasonal influenza vaccine for adults and children in preventing laboratory-confirmed influenza in primary care in the United Kingdom: 2015/16 end-of-season results. Euro Surveill. 2016;21(38).
  3. Nohynek H, Baum U, Syrjanen R, Ikonen N, Sundman J, Jokinen J. Effectiveness of the live attenuated and the inactivated influenza vaccine in two-year-olds - a nationwide cohort study Finland, influenza season 2015/16. Euro Surveill. 2016;21(38).
  4. Kissling E, Valenciano M. Early influenza vaccine effectiveness results 2015–16: I-MOVE multicentre case-control study. Eurosurveillance. 2016;21(6).
  5. World Health Organization. Recommended composition of influenza virus vaccines for use in the 2016-2017 northern hemisphere influenza season2016 25 Feb 2016. Available from: http://www.who.int/influenza/vaccines/virus/recommendations/201602_recommendation.pdf.
  6. European Centre for Disease Prevention and Control/WHO Regional Office for Europe. Flu News Europe, Joint ECDC–WHO weekly influenza update, week​ 20/2016.2016 5 October 2016. Available from: http://flunewseurope.org/Archives.

 

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