Influenza virus activity in the world

25 May 2012

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

Based on FluNet reporting (as of 22 May 2012, 13:00 UTC), during weeks 18 to 19 (29 April 2012 to 12 May 2012), National Influenza Centres (NICs) and other national influenza laboratories from 83 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 26 758 specimens. 3 540 were positive for influenza viruses, of which 2 366 (66.8%) were typed as influenza A and 1 174 (33.2%) as influenza B. Of the sub-typed influenza A viruses, 190 (10.1%) were influenza A(H1N1)pdm09 and 1 691 (89.9%) were influenza A(H3N2). Of the characterized B viruses, 45 (67.2%) belong to the B-Yamagata lineage and 22 (32.8%) to the B-Victoria lineage.


During weeks 18 and 19 in 2012, laboratory confirmed influenza activity in general was low worldwide. Influenza A(H3N2) remained as the predominant virus subtype detected globally except in a number of countries where influenza B virus was dominant. Influenza A(H1N1)pdm09 virus was detected in low numbers globally.

In Asia, influenza A(H3N2) viruses were predominant in China and China Hong Kong Special Administrative Region. Influenza B was the main virus detected in in Japan and the Republic of Korea, while A(H1N1)pdm09 and influenza B viruses co-circulated in similar proportions in India.

In Europe, the number of influenza virus detections continued to decline. Influenza A(H3N2) remained the dominant virus in circulation but a higher prevalence of influenza B viruses was detected than in previous weeks.

In North America, influenza activity decreased in both Canada and the United States of America. Influenza B and A(H3N2) viruses remained the predominant virus subtypes in these countries respectively. The proportion of influenza B viruses detected in the United States of America continued to increase.

In Central America increased influenza A(H3N2) virus activity was reported in the Dominican Republic. Influenza A(H1N1)pdm09 virus was the predominant virus subtype detected in El Salvador and Honduras.

In the southern hemisphere, influenza activity remained low. Influenza A(H1N1)pdm09, A(H3N2) and B viruses were detected sporadically in Africa and Oceania. In South America, influenza B viruses virus continued to circulate in the Plurinational State of Bolivia while the predominant virus in Chile was A(H3N2).

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