Influenza

Influenza virus activity in the world

30 March 2012

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

Based on FluNet reporting (as of 27 March 2012, 14:00 UTC) during weeks 10 to 11 (4 March 2012 to 17 March 2012), National Influenza Centres (NICs) and other national influenza laboratories from 88 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 50,919 specimens. 15,214 were positive for influenza viruses, of which 11,559 (76%) were typed as influenza A and 3,655 (24%) as influenza B. Of the sub-typed influenza A viruses, 957 (15%) were influenza A(H1N1)pdm09 and 5,351 (85%) were influenza A(H3N2). Of the characterized B viruses, 420 (45%) belong to the B-Yamagata lineage and 509 (55%) to the B-Victoria lineage.

Summary

During weeks 10 and 11 in 2012, laboratory confirmed influenza activity continued to increase in many countries in the northern hemisphere with regional and widespread outbreaks reported in a number of countries.

Influenza A(H3N2) continued to be the predominant virus subtype detected globally. In general, influenza A(H1N1)pdm09 remained low with the exception of a few countries. Influenza B virus activity was high in a number of countries and was the predominant virus detected in Canada and China.

In Europe, outbreaks of influenza A(H3N2) were reported with increasing co-circulation of influenza B in some countries. In northern Africa, influenza A(H3N2) activity decreased with local outbreaks reported only in Algeria.

In the United States of America, influenza A(H3N2) remained the predominant virus subtype while in Canada influenza B detections continued to increase and surpassed the number of influenza A viruses reported. A(H1N1)pdm09 viruses remained the predominant virus subtype in Mexico. A(H1N1)pdm09 viruses were reported in increasing proportions in some regions in the United States of America. In Central America, influenza activity increased in Guatemala with A(H1N1)pdm09 viruses the main circulating virus subtype.

In Asia, A(H3N2) and B virus influenza activity remained high, with B viruses predominating in China, China Hong Kong Special Administrative Region and the Republic of Korea. Influenza A(H3N2) viruses remained predominant in Japan with some co-circulation of influenza B. In the Middle East, A(H1N1)pdm09 activity increased in Qatar.

In the southern hemisphere, influenza activity continued to be low with the majority of the sporadic virus detections identified as influenza A(H3N2).

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Snapshot global influenza virus circulation (GISRS-FluNet, 27 March 2012)