From Pro-MED mail we have the latest Flu reports released by the World Health Organization in relation to the Northern Hemisphere flu season.

Summary
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The patterns of influenza activity remain diverse across the WHO European Region. Consultation rates for influenza-like illness (ILI) and/or acute respiratory infection (ARI) are increasing in the majority of countries in the Region, including eastern Europe, but have started to decrease in northern countries. Influenza A(H1N1)pdm09, A(H3N2) and type B viruses are circulating in the Region, but the relative proportion of influenza A(H1N1)pdm09 in samples from sentinel and non-sentinel sources continues to increase. The number of reported hospitalizations due to severe acute respiratory infection (SARI) is increasing slowly in association with the increase in influenza activity in the eastern part of the Region

Virological surveillance for influenza
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The number of specimens testing positive for influenza in the Region was similar to the previous week, again mainly due to detections in the western part of the Region. Overall, a total of 3741 specimens tested positive for influenza in week 3/2013, which 2840 (76 percent) were influenza A.

For week 3/2013 the picture related to the proportion of influenza A(H1N1)pdm09 viruses versus A(H3N2) was similar to those in the 2 previous weeks, with A(H1N1)pdm09 dominating: of 1856 influenza A viruses subtyped, 1488 (80 percent) were A(H1N1)pdm09 while 368 (20 percent) were A(H3N2).


Since the beginning of the season (week 40/2012), 16 457 influenza viruses from sentinel and non-sentinel sources have been typed: 11 318 (69 percent) were influenza A and 5 139 (31 percent) influenza B. Of the influenza A viruses, 6698 were subtyped: 4552 (68 percent) as A(H1N1)pdm09 and 2146 (32 percent) as A(H3N2). In addition, since week 40/2012, the lineage for 788 influenza B viruses has been determined: 707 (90 percent) belonged to the B/Yamagata lineage and 81 (10 percent) to B/Victoria.

The circulation of influenza viruses remains variable across the Region. Influenza A (mainly A(H1N1)pdm09) continues to be reported as the dominant virus in an increasing number of countries in northern and central Europe, the Russian Federation and Turkey, while influenza B is reported as the dominant virus in some countries in the southern and western parts of the Region. Between these areas, co-circulation of A(H1N1)pdm09, A(H3N2) and influenza B is reported.

Virus strain characterisations
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For the 2012/2013 northern hemisphere influenza season, the WHO recommends inclusion of A/California/7/2009 (H1N1)pdm09-like, A/Victoria/361/2011 (H3N2)-like and B/Wisconsin/1/2010-like (from the B/Yamagata lineage) viruses in vaccines. The majority of characterized viruses from the WHO European Region have been similar to these vaccine viruses.

Since week 40/2012, 964 influenza viruses characterized antigenically by 10 countries (Denmark, the United Kingdom (England), Germany, Latvia, Portugal, Romania, the Russian Federation, Scotland, Slovakia, Switzerland) corresponded with the viruses recommended by WHO for inclusion in the current northern hemisphere seasonal influenza vaccine.

11 countries (Austria, Belgium, Denmark, Finland, Germany, Norway, Portugal, Scotland, Spain, Sweden, Switzerland) have characterized 240 influenza viruses genetically. At present, both A(H1N1)pdm09 and A(H3N2) viruses fall into a number of different genetic groups, but they remain antigenically similar to their respective vaccine viruses, A/California/7/2009 and A/Victoria/361/2011.

Influenza B viruses of the B/Victoria/2/87 and the B/Yamagata/16/88 lineages are co-circulating with the clear dominance of the B/Yamagata lineage viruses this season. Influenza B viruses of the B/Victoria lineage, all fall within the B/Brisbane/60/2008 clade and are antigenically indistinguishable. B/Yamagata lineage viruses in circulation clearly fall into 2 distinct genetic clades, 2 and 3 represented by B/Estonia/55669/2011 and B/Wisconsin/1/2010 respectively. Viruses in these clades can be distinguished antigenically from each other, but the antigenic differentiation of these clades is not clear-cut as post-infection ferret antisera raised against clade 2 viruses are more clade-specific than are antisera raised against clade 3 viruses. Nevertheless, viruses within these clades remain antigenically similar to the current vaccine strain.

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26 Jan 2013 Influenza (10): European region update