Influenza

Influenza virus activity in the world

20 January 2012

Source: Laboratory confirmed data from the Global Influenza Surveillance and Response System (GISRS).

Based on FluNet reporting (as of 17 January 2012, 13:40 UTC), during week 52 in 2011 and week 1 in 2012 (25 December 2011 to 7 January 2012), National Influenza Centres (NICs) and other national influenza laboratories from 81 countries, areas or territories reported data to FluNet. The WHO GISRS laboratories tested more than 27410 specimens. 3148 (11%) were positive for influenza viruses, of which 1759 (56%) were typed as influenza A and 1389 (44%) as influenza B. Of the sub-typed influenza A viruses, 142 (10%) were influenza A(H1N1)pdm09 and 1326 (90%) were influenza A(H3N2). Of the characterized B viruses, 419 (68%) belong to the B-Yamagata lineage and 199 (32%) to the B-Victoria lineage.

Summary

During week 52 in 2011 and week 1 in 2012, laboratory confirmed influenza activity continued to increase in some countries in the northern hemisphere but in general influenza activity remained low.

Globally influenza A(H3N2) remained the predominant virus subtype detected. Influenza A(H1N1)pdm09 detection was very low, while the proportion of circulating B virus varied. Co-circulation of both B/Yamagata and B/Victoria lineage viruses were reported in some countries.

In Europe, the Middle East, North Africa and North America, influenza A(H3N2) activity continued to increase in some countries with localized to widespread activity reported. Influenza B virus was detected at low levels with A(H1N1)pdm09 detected sporadically.

In Asia, activity of influenza viruses in various proportions increased in some countries ranging from local to regional levels. Influenza A(H3N2) virus predominated in Japan and the Republic of Korea, while influenza B predominated in China. In some other countries, A(H3N2) and B co-circulated. Influenza A(H1N1)pdm09 was detected at very low levels.

In the southern hemisphere, influenza activity remained low with influenza A(H3N2) virus predominating.

A new candidate A(H5N1) reassortant vaccine virus has been developed from A/Hubei/1/2010 (H5N1) which belongs to clade 2.3.2.1, and is available for distribution on request:

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Snapshot global influenza virus circulation (GISRS-FluNet, 17 January 2011)