Influenza virus characterisation - July 2012

Since 1 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 remain antigenically similar to it.
During this time period, all European 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 propagated exclusively 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, represented by B/Bangladesh/3333/2007 and B/Wisconsin/1/2010 (Clade 3) or B/Brisbane/3/2007 (Clade 2); viruses in these clades are antigenically distinguishable.
Antigenic analysis of A(H3N2)v viruses, the cause of zoonotic infections in the USA, indicate that they are antigenically distinct from seasonal A(H3N2) viruses.