Influenza

Influenza virus activity in the world

3 February 2012

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

Based on FluNet reporting (as of 31 January 2012, 13:35 UTC), during weeks 2 to 3 (8 – 21 January 2012), National Influenza Centres (NICs) and other national influenza laboratories from 84 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 31292 specimens. 4709 were positive for influenza viruses, of which 3633 (77.2%) were typed as influenza A and 1076 (22.8%) as influenza B. Of the sub-typed influenza A viruses, 668 (22.9%) were influenza A(H1N1)pdm09 and 2250 (77.1%) were influenza A(H3N2). Of the characterized B viruses, 90 (33.5%) belong to the B-Yamagata lineage and 179 (66.5%) to the B-Victoria lineage.

Summary

During weeks 2 and 3 in 2012, laboratory confirmed influenza activity continued to increase in many countries in the northern hemisphere but in general influenza activity remained mild.

Globally influenza A(H3N2) continued to be the predominant virus subtype detected. In general, influenza A(H1N1)pdm09 and B activity was low, except for Mexico with A(H1N1)pdm09 predominating and for some Asian countries with B as main circulating virus type. Both B/Yamagata and B/Victoria lineage viruses co-circulated, the majority of viruses detected belong to the B/Victoria lineage.

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

In Asia, influenza activity of A(H3N2) and B viruses continued to increase in many countries, with B viruses predominating in China and China Hong Kong Special Administrative Region, and A(H3N2) viruses in many other countries. Influenza A(H1N1)pdm09 was detected at low levels.

In the southern hemisphere, influenza activity remained low. Among sporadic detections, the majority are influenza A(H3N2) viruses.

A human case of influenza A(H5N1) virus infection was reported in China. The virus belongs to clade 2.3.4.2, and is expected to be sensitive to NAIs and adamantanes by sequencing. Further analysis of the virus including its antigenic relationship with developed candidate reassortant vaccine viruses is being conducted by the WHO Collaborating Centre for Reference and Research on Influenza at the Chinese Center for Disease Control and Prevention.

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Snapshot global influenza virus circulation (GISRS-FluNet, 31 January 2012)