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1 Mar 2013

Influenza virus activity in the world (WHO, March 1 2013, edited)

[Source: World Health Organization, full page: (LINK). Edited.]

Influenza virus activity in the world

1 March 2013

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


Based on FluNet reporting (as of 26 February 2013, 11:00 UTC), during weeks 6 to 7 (3 February 2013 to 16 February 2013), National Influenza Centres (NICs) and other national influenza laboratories from 82 countries, areas or territories reported data.

The WHO GISRS laboratories tested more than 69 936 specimens.

20 972 were positive for influenza viruses, of which 14 140 (67.4%) were typed as influenza A and 6 832 (32.6%) as influenza B.

Of the sub-typed influenza A viruses, 5 982 (64.1%) were influenza A(H1N1)pdm09 and 3 344 (35.9%) were influenza A(H3N2).

Of the characterized B viruses, 485 (91.5%) belong to the B-Yamagata lineage and 45 (8.5%) to the B-Victoria lineage.



During weeks 6 to 7, influenza activity remained high in the northern hemisphere and sporadic in the southern hemisphere. A(H1N1)pdm09 viruses predominated, followed by A(H3N2) and influenza B viruses.

In North America, laboratory confirmed detections of influenza A viruses decreased while the number of influenza B viruses detected increased compared to previous weeks. A(H3N2) remained the predominant virus subtype. One case of A(H1N1)pdm09 virus with reduced susceptibility to oseltamivir was reported in the United States of America, bringing the total number of cases reported since 1 October 2012 to two.

Influenza activity across the European region remained variable. Increased influenza activity was reported in countries from eastern Europe, while activity continued to decrease in the northern and western European countries. A(H1N1)pdm09 viruses remained the predominant virus circulating throughout most of the region. A few countries reported influenza B as the predominantly circulating virus.

In Asia, A(H1N1)pdm09 viruses were the predominant subtype and co-circulated with A(H3N2) in a number of countries. However, in some countries, A(H3N2) viruses were the predominant subtype and co-circulated with A(H1N1)pdm09 and influenza B viruses.

Sporadic detections of A(H1N1)pdm09, A(H3N2) and influenza B viruses were reported from the Caribbean, Central and South America. In general, A(H3N2) viruses were the predominant virus reported in South America. In Oceania, Australia reported sporadic influenza activity of A(H1N1)pdm09, A(H3N2) and influenza B viruses.

In Africa sporadic detections of A(H1N1)pdm09, A(H3N2) and influenza B viruses were reported. Increased detections of influenza B virus relative to A(H1N1)pdm09 were reported from northern Africa.

Following the WHO Consultation on the Composition of Influenza Virus Vaccines for the Northern Hemisphere held from 18 to 20 February 2013, it is recommended that influenza vaccines for the northern hemisphere 2013-2014 season contain the following viruses :

  • an A/California/7/2009 (H1N1)pdm09-like virus;
  • an A(H3N2) virus antigenically like the cell-propagated prototype virus A/Victoria/361/2011*;
  • a B/Massachusetts/2/2012-like virus.

For quadrivalent vaccines containing two influenza B viruses, it is recommended to include a B/Brisbane/60/2008-like virus in addition to the above three viruses.

* It is recommended that A/Texas/50/2012 is used as the A(H3N2) vaccine component due to antigenic changes in earlier A/Victoria/361/2011-like vaccine viruses (such as IVR-165) resulting from adaptation to propagation in eggs.


For more information: Recommended composition of influenza virus vaccines for use in the 2013-14 northern hemisphere influenza season

A list of updated candidate vaccine viruses and reagents can be found at: