WHO recommendations for influenza virus vaccine composition for the 2015 southern hemisphere season

ECDC comment

​The World Health Organization (WHO) ha.s agreed on the recommended composition of the trivalent influenza vaccine for the southern hemisphere winter 2015 influenza season.

​World Health Organization, Geneva, Switzerland – 25rd September 2014, report

The World Health Organization (WHO) has agreed on the recommended composition of the trivalent influenza vaccine for the southern hemisphere winter 2015 influenza season as:

- A/California/7/2009 (H1N1)pdm09-like virus;- A/Switzerland/9715293/2013 (H3N2)-like virus; and - B/Phuket/3073/2013-like virus (Yamagata lineage).


For quadrivalent vaccines containing two influenza B viruses, the above three viruses and a B/Brisbane/60/2008-like virus (Victoria lineage) should be included.

With this recommendation, two of the vaccine components, the A(H3N2) and B virus,  will be changed in the trivalent vaccines in comparison to the equivalent vaccine last year. The reason for the change is that increasing proportions of the circulating A(H3N2) and B Yamagata-lineage viruses have undergone antigenic drift since the last vaccine recommendation [1]. All the (sub)types of influenza viruses have been circulating in the southern hemisphere with variable levels of activity. Further antigenic and genetic characteristics of recent seasonal influenza viruses are described below[2].  

Influenza A(H1N1)pdm09 viruses

The A(H1N1)pdm09 viruses remain antigenically homologous and closely related to the earlier vaccine virus A/California/7/2009 and therefore there is no change in the recommendation for this component. The sequence analysis of the haemagglutinin (HA)genes of A(H1N1)pdm09 viruses indicated that the viruses fell within two genetic groups, genetic clades 6 and 7, which are antigenically indistinguishable.
Influenza A(H3N2) viruses

Many of the A(H3N2) viruses circulating from February to September 2014 have shown antigenic drift from the earlier vaccine viruses A/Victoria/361/2011 and A/Texas/50/2012 (the northern hemisphere 2014-2015 vaccine component).  Therefore the recommendation is to change the A(H3N2) vaccine component to a virus representing more closely the recently circulating viruses. The recent viruses are represented by an A/Switzerland/9715293/2013 (H3N2)-like virus in the new recommendation.

The recently circulating viruses were not well recognised by ferret antisera raised against cell-propagated reference viruses such as A/Texas/50/2012 and A/Victoria/361/2011 being inhibited in HI assays at a lower titre of antiserum. The HA genes of recent A(H3N2) viruses fell into two new main phylogenetic groups that were both antigenically distinguishable from previously circulating viruses.

Influenza B viruses

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

The majority of circulating viruses of the B/Yamagata/16/88 lineage fell genetically within two groups, clades 2 and 3, with the majority collected in February 2014 falling in clade 3. In this group some virus reassortants were observed with the neuraminidase (NA) gene from the B/Victoria lineage. The proportion of these reassortant viruses is increasing in several parts of the world.  The recent B/Yamagata viruses that fell into the predominating clade, clade 3, were antigenically distinguishable from the previous vaccine virus of the B/Yamagata/16/88 lineage (B/Massachusetts/2012). The recently circulating viruses are at the moment best represented by viruses that are B/Phuket/3073/2013-like.

The majority of viruses of the B/Victoria/2/87 lineage were antigenically closely related to the earlier vaccine virus B/Brisbane/60/2008. That virus has been recommended as a component of the quadrivalent vaccines in the southern hemisphere. There was no antigenic drift observed in the B/Victoria –lineage viruses. The recommendation for the B/Victoria-lineage vaccine component has not changed in comparison to the recommendation for the northern hemisphere 2014-2015 influenza seasonal vaccine recommendation [3] or for the 2014 southern hemisphere influenza season [4].

ECDC comment:

The antigenic drift in the A(H3N2) and B/Yamagata viruses may indicate that the northern hemisphere vaccine may not give an optimal protection against the A(H3N2) and B/Yamagata viruses in the 2014-2015 influenza season in temperate countries.
Based on the laboratory results for A(H3N2) viruses, it is not straightforward to predict the match with the circulating viruses because the post-infection ferret antisera raised against typical A(H3N2) viruses in circulation in 2013 recognise the new A(H3N2) viruses at low titre. Therefore, partial protection by the northern hemisphere vaccine against the circulating viruses in season 2014-2015 should be assumed.  Furthermore, sufficient antigenic homology exists between the B/Yamagata clade 2 and 3 viruses and therefore it is likely that the northern hemisphere vaccine B/Yamagata component would protect against the currently circulating viruses of genetic clade 3 as well. Vaccine effectiveness was only moderate against A(H1N1)pdm09 and low against A(H3N2) during the last season[5,6]. However, ECDC considers the seasonal influenza vaccination still the most effective single measure to prevent influenza.
References:1. WHO. Questions and Answers. Recommended composition of influenza virus vaccines for use in the southern hemisphere 2015 influenza season and development of candidate vaccine viruses for pandemic preparedness 2014. Available from: http://www.who.int/influenza/vaccines/virus/recommendations/201409_qanda_recommendation.pdfua=1.2. WHO. Recommended composition of influenza virus vaccines for use in the 2015 southern hemisphere influenza season 2014. Available from: http://www.who.int/influenza/vaccines/virus/recommendations/201409_recommendation.pdf.3. WHO. Recommended composition of influenza virus vaccines for use in the 2014-2015 northern hemisphere influenza season. 2014. Available from: http://www.who.int/influenza/vaccines/virus/recommendations/2014_15_north/en/.4. WHO. Recommended composition of influenza virus vaccines for use in the 2014 southern hemisphere influenza season 2013. Available from: http://www.who.int/influenza/vaccines/virus/recommendations/2014_south/en/.5. Castilla J, Martinez-Baz I, Navascues A, Fernandez-Alonso M, Reina G, Guevara M, et al. Vaccine effectiveness in preventing laboratory-confirmed influenza in Navarre, Spain: 2013/14 mid-season analysis. Euro Surveill. 2014;19(6).6. McNeil S, Shinde V, Andrew M, Hatchette T, Leblanc J, Ambrose A, et al. Interim estimates of 2013/14 influenza clinical severity and vaccine effectiveness in the prevention of laboratory-confirmed influenza-related hospitalisation, Canada, February 2014. Euro Surveill. 2014;19(9).
Prepared by Eeva Broberg, ECDCReviewed by Emmanuel Robesyn, Kari Johansen, Piotr Kramarz and Pasi Penttinen (ECDC) and John McCauley (WHO CC, London).