Influenza virus activity in the world
11 May 2012
Based on FluNet (as of 7 May 2012, 10:00 UTC), during weeks 16 to 17 (15 April 2012 to 28 April 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 30 585 specimens. 5 297 were positive for influenza viruses, of which 3 343 (63.1%) were typed as influenza A and 1 954 (36.9%) as influenza B. Of the subtyped influenza A viruses, 308 (13.4%) were influenza A(H1N1)pdm09 and 1 982 (86.6%) were influenza A(H3N2). Of the characterized B viruses, 85 (37.6%) belonged to the B-Yamagata lineage and 141 (62.4%) to the B-Victoria lineage.
During weeks 16 and 17 in 2012, laboratory confirmed influenza activity in general was low worldwide. Activity continued to decline in the northern hemisphere.
Influenza A(H3N2) remained the predominant virus subtype detected globally at low levels except in a number of countries where influenza B was dominant virus. Influenza A(H1N1)pdm09 virus was detected to a lesser extent.
In Europe, the number of virus detections declined. Influenza A(H3N2) continued to be the dominant virus in circulation, followed by influenza B.
In North America, influenza A(H3N2) remained the predominant virus subtype in the United States of America, with an increasing proportion of B viruses relative to influenza A viruses observed in recent weeks. Influenza B continued to be the main virus detected in Canada. In Central America influenza activity was low, except in the Dominican Republic where outbreaks of influenza A(H3N2) virus continued to be reported.
In Asia, influenza A(H3N2) and B viruses co-circulated in China, China Hong Kong Special Administrative Region and a number of other countries and areas. Influenza B virus predominated in Japan and the Republic of Korea, while in India both A(H1N1)pdm09 and influenza B viruses co-circulated. Influenza A(H1N1)pdm09 continued to be the main virus detected in Qatar in the Middle East.
In the southern hemisphere, influenza activity remained low with the majority of the virus detections identified as influenza A(H3N2). An increase of influenza B virus activity was observed in the Plurinational State of Bolivia with limited co-circulation of influenza A(H1N1)pdm09 virus.