WHO recommendations for the viruses to be used in the 2012 Southern Hemisphere Influenza Vaccine: epidemiology, antigenic and genetic characteristics of influenza A(H1N1)pdm09, A(H3N2) and B influenza viruses collected from February to September 2011

Abstract

In February and September each year the World Health Organisation (WHO) recommends influenza viruses to be included in influenza vaccines for the forthcoming winters in the Northern and Southern Hemispheres respectively. These recommendations are based on data collected by National Influenza Centres (NIC) through the Global Influenza Surveillance and Response System (GISRS) and a more detailed analysis of representative and potential antigenically variant influenza viruses from the WHO Collaborating Centres for Influenza (WHO CCs) and Essential Regulatory Laboratories (ERLs). This article provides a detailed summary of the antigenic and genetic properties of viruses and additional background data used by WHO experts during development of the recommendations for the 2012 Southern Hemisphere influenza vaccine composition.

Fig. 1

Maps showing peak levels of laboratory confirmed influenza (reported to FluNet) in each country with an NIC, for the period February to September 2011: a) A(H1N1)pdm09 viruses; b) A(H3N2) viruses; c) B viruses. The total number of seasonal and pandemic viruses detected by GISRS from February to September 2011 for each type/subtype is shown in panels: d) A(H1N1)pdm09; e) A(H3N2); f) B viruses.

Fig. 2

Phylogenetic trees of representative A(H1N1)pdm09 HA1 domain nucleotide sequences were constructed with the PhyML software package 3.0 [7] using GTR+I+Γ4 as determined by ModelTest [8]. GARLI v0.961 [9] was run on the best tree from PhyML for 2 million generations to optimise tree topology and branch lengths. Amino acid substitutions are marked on major nodes. Viruses are colour-coded by month of collection as follows: March-April 2011 in Blue, May 2011 in Green, June – July 2011 in Orange, August 2011 in Pink. The current vaccine strain is in Red. Genetic subgroups are labelled 1–8.

Fig. 3

An antigenic map [10] generated from A(H1N1)pdm09 HI data from WHO CCs in Atlanta, London, Melbourne and Tokyo from April 2009 – August 2011. Viruses are represented as circles, antisera as squares. The current vaccine strain A/California/7/2009 is represented by the large green dot, 2011 viruses with 8-fold or greater reductions in HI titres to the A/California/7/2009 ferret antiserum are in red, the remaining 2011 viruses in blue. The Grid indicates a 2-fold dilution in HI titre, 1 unit of antigenic distance [10].

Fig. 4

Phylogenetic trees of representative A(H3N2) HA1 domain nucleotide sequences were constructed and annotated as described for Fig. 2. Genetic subgroups are labelled 1–7.

Fig. 5

Phylogenetic trees of representative B/Victoria lineage HA1 domain nucleotide sequences were constructed and annotated as described for Fig. 2. Genetic groups are labelled 1–7.