Influenza

Influenza virus activity in the world

2 March 2012

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

Based on FluNet reporting (as of 28 February 2012, 12:10 UTC) during weeks 6 to 7 (5 February 2012 to 18 February 2012), National Influenza Centres (NICs) and other national influenza laboratories from 79 countries, areas or territories reported data to FluNet. The WHO GISRS laboratories tested more than 45 853 specimens. 12 748 were positive for influenza viruses, of which 8 624 (67.6%) were typed as influenza A and 4 124 (32.4%) as influenza B. Of the sub-typed influenza A viruses, 858 (15.9%) were influenza A(H1N1)pdm09 and 4 533 (84.1%) were influenza A(H3N2). Of the characterized B viruses, 547 (38.5%) belong to the B-Yamagata lineage and 872 (61.5%) to the B-Victoria lineage.

Summary

During weeks 6 and 7 in 2012, laboratory confirmed influenza activity continued to increase in many countries in the northern hemisphere with localized to widespread activity occurring.

Globally influenza A(H3N2) persisted to be the predominant virus subtype detected. In general, influenza A(H1N1)pdm09 was low, except in Mexico and a few areas in Canada and the United States of America where A(H1N1)pdm09 was the predominant virus. Influenza B virus activity was also low with the exception of some Asian countries where it continued to be the main circulating virus type. The number of B/Yamagata lineage viruses relative to the B/Victoria-like viruses increased compared to the previous reporting period.

In Europe influenza A(H3N2) activity continued to increase in many countries and was the predominant virus circulating in North America. Regional outbreaks of influenza A(H3N2) were reported in some countries in northern Africa. Influenza B virus was detected at low levels with A(H1N1)pdm09 detected only sporadically.

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

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

WHO recommendation of influenza virus vaccine composition for the northern hemisphere 2012-2013

Comprehensive analysis of antigenic and genetic characterization of influenza viruses received in the WHO GISRS was conducted during a WHO consultation held from 20 - 23 February 2012. Based on the analysis, as advised by an advisory group of 9 experts, WHO recommends the 3 viruses below for use in the vaccines for northern hemisphere 2012-2013:

  • an A/California/7/2009 (H1N1)pdm09-like virus;
  • an A/Victoria/361/2011 (H3N2)-like virus;
  • a B/Wisconsin/1/2010-like virus .

In addition, a review of the selection and development of candidate vaccine viruses, including H5 and H9, for pandemic preparedness was also conducted and a summary report has been published.

Other analyses

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Snapshot global influenza virus circulation (GISRS-FluNet, 28 February 2012)