Influenza virus characterisation - Summary Europe, June 2012

Surveillance report
Publication series: Influenza Virus Characterisation

Since 01 January 2012, influenza A(H1N1)pdm09, influenza A(H3N2), and influenza B/Victoria- and B/Yamagata-lineage viruses have been detected in ECDC-affiliated countries.
Type A viruses have predominated over type B.
A(H3N2) viruses have predominated over A(H1N1)pdm09 viruses.
A(H1N1)pdm09 viruses continue to show genetic drift from the vaccine virus, A/California/07/2009, but the vast majority are antigenically similar to A/California/07/2009.
During this time period, all A(H3N2) viruses sequenced fell within five genetic groups. Test viruses isolated in mammalian cells show low titres with post-infection ferret antisera raised against egg-propagated viruses, including the new vaccine virus A/Victoria/361/2011. They react well with post-infection ferret antisera raised against A/Victoria/361/2011 and other current reference viruses exclusively propagated in tissue culture.
Recent B/Victoria lineage viruses fell within the B/Brisbane/60/2008 genetic clade and were antigenically similar to reference cell-propagated viruses of the B/Brisbane/60/2008 genetic clade.
Recent B/Yamagata-lineage viruses fell into two genetic clades, the B/Bangladesh/3333/2007 and B/Wisconsin/1/2010 genetic clade or into the B/Brisbane/3/2007 genetic clade; viruses in these clades are antigenically distinguishable.

Executive summary

The latest issue of ECDC’s series of technical documents on 'Influenza virus characterisation’ covers the time period from January 2012 to June 2012.

In the first six months of the year, the WHO Collaborating Centre for Reference and Research on Influenza at the MRC National Institute for Medical Research in London received and analysed a total of 426 virus samples, submitted by 23 EU/EAA countries. The results showed that all A(H3N2) viruses sequenced fell within five genetic groups, and that these groups have predominated over A(H1N1)pdm09 viruses.

Following further details on the analysis of influenza A(H1N1)pdm09 and influenza A(H3N2) viruses, the report provides eight phylogenetic tree charts, produced by the Community Network of Reference Laboratories (CNRL) for Human Influenza in Europe, that graphically represent the proportion of nucleotide changes in the viruses’ DNA sequence. The tree charts are supplemented by several tables that list the results of the antigenic analyses of several virus types, including the now-dominant A(H3N2) viruses.