Influenza virus activity in the world

14 September 2012

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

Based on FluNet reporting (as of 11 September 2012, 12:40 UTC), during weeks 34 to 35 (19 August 2012 to 1 September 2012), National Influenza Centres (NICs) and other national influenza laboratories from 78 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 14 677 specimens. 1 870 were positive for influenza viruses, of which 1 293 (69.1%) were typed as influenza A and 577 (30.9%) as influenza B. Of the sub-typed influenza A viruses, 171 (14.2%) were influenza A(H1N1)pdm09 and 1 020 (84.6%) were influenza A(H3N2). Of the characterized B viruses, 16 (69.6%) belong to the B-Yamagata lineage and 7 (30.4%) to the B-Victoria lineage.


During weeks 34 and 35, influenza activity continued to decrease compared to recent weeks in the southern hemisphere. Influenza A(H3N2) viruses remained the predominant subtype globally, followed by influenza B and A(H1N1)pdm viruses.

Influenza activity decreased in the Oceania region. Australia and New Zealand reported fewer laboratory confirmed influenza positives of the circulating subtypes while sporadic activity was reported from New Caledonia.

Influenza B viruses were the predominant virus detected in the African region and sporadic detections of A(H3N2) viruses were also reported from the region. Influenza activity remained high in South Africa with co-circulation of A(H3N2) and influenza B viruses.

In southern mainland China, influenza activity began to decrease. Influenza A(H3N2), A(H1N1)pdm09 and influenza B viruses were reported from the region while A(H3N2) remained the predominant subtype in the region.

Influenza activity remained low in central and South America with fewer detections of A(H1N1)pdm, A(H3N2) and influenza B viruses reported by the region.

Sporadic detections of A(H3N2) and influenza B viruses were reported from the European region. Two independent cases of A(H1N1)pdm viruses carrying the H275Y mutation associated with oseltamivir resistance were reported from Netherlands. Partial sequencing of the NA, HA, PB2 and M genes revealed that the viruses were identical.

In North America influenza activity remained low. To date, 296 cases of infection with the variant A(H3N2)v viruses have been detected in the United States of America with 16 cases hospitalized and 1 death reported.

A(H1N2) variant viruses have also been recently reported from Minnesota in the United States of America. These A(H1N2) variant viruses are very similar to those found in humans previously but differ as they have the M gene derived from the A(H1N1)pdm09 virus. This is the first time this variant virus has been isolated from humans.

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