Influenza virus activity in the world

16 March 2012

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

Based on FluNet reporting (as of 13 March 2012, 12:30 UTC) during weeks 8 to 9 (19 February 2012 to 3 March 2012), National Influenza Centres (NICs) and other national influenza laboratories from 89 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 46 916 specimens. 14 235 were positive for influenza viruses, of which 10 965 (77%) were typed as influenza A and 3 270 (23%) as influenza B. Of the sub-typed influenza A viruses, 794 (13.2%) were influenza A(H1N1)pdm09 and 5 234 (86.8%) were influenza A(H3N2). Of the characterized B viruses, 475 (47.5%) belong to the B-Yamagata lineage and 525 (52.5%) to the B-Victoria lineage. This represents an increase in the proportion of viruses belonging to the B-Yamagata lineage versus B-Victoria lineage compared to the previous reporting period.


During weeks 8 and 9 in 2012, laboratory confirmed influenza activity continued to increase in many countries in the northern hemisphere.

Influenza A(H3N2) remained the predominant virus subtype detected globally. In general, influenza A(H1N1)pdm09 was low. Influenza B virus activity increased in a number of countries and remained the main circulating virus type in China. In Europe, regional and widespread outbreaks of influenza A(H3N2) were reported with increasing co-circulation of influenza B in some countries.

In Canada and the United States of America, influenza A(H3N2) continued to circulate but an increased number of influenza B viruses were detected than in the previous reporting period. B viruses from both B/Yamagata and B/Victoria-like lineages were detected in approximately equal proportions in both of these countries. A(H1N1)pdm09 viruses continued to be detected only sporadically with the exception of Mexico where local activity was reported.

In Asia, A(H3N2) and B virus influenza activity continued to increase, with B viruses predominating in China and China Hong Kong Special Administrative Region. Influenza A(H3N2) viruses remained predominant in Japan but at much lower levels than in previous weeks. Influenza A(H1N1)pdm09 was detected at very low levels in a number of countries.

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

A comprehensive report on the WHO recommendations for the influenza virus vaccine composition for the northern hemisphere 2012-2013 has been published in the Weekly Epidemiological Record:

A "Questions and Answers" document concerning the updated recommendations for influenza virus vaccines for use in the 2012-2013 northern hemisphere influenza season has been recently published on the WHO web.

The review of the selection and development of candidate vaccine viruses, including A(H5N1) and A(H9N2), for pandemic preparedness has also been published in the Weekly Epidemiological Record:

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