Influenza virus activity in the world

17 August 2012

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

Based on FluNet reporting (as of 14 August 2012, 13:00 UTC), during weeks 30 to 31 (22 July 2012 to 4 August 2012), National Influenza Centres (NICs) and other national influenza laboratories from 67 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 15 161 specimens. 2 670 were positive for influenza viruses, of which 2 168 (81.2%) were typed as influenza A and 502 (18.8%) as influenza B. Of the sub-typed influenza A viruses, 172 (8.5%) were influenza A(H1N1)pdm09 and 1842 (91.5%) were influenza A(H3N2). Of the characterized B viruses, 3 (30%) belong to the B-Yamagata lineage and 7 (70%) to the B-Victoria lineage.


During weeks 30 and 31, with variable levels of influenza activity reported, a decrease was observed in general in the southern hemisphere, where A(H3N2) remained as the predominant virus subtype detected followed by influenza B and A(H1N1)pdm09.

Sporadic influenza activity was reported from the African region. Decreasing activity of A(H3N2) and influenza B viruses was reported from Madagascar and South Africa while A(H1N1)pdm09 viruses were detected in Côte d’Ivoire and Democratic Republic of the Congo.

In Oceania, the number of influenza A(H3N2) detections began to decrease in New Zealand while local outbreaks of A(H3N2) viruses continued in Australia.

In South and Central America, influenza activity decreased. Sporadic detections of A(H1N1)pdm09 viruses were reported with influenza B the predominant virus type. However, during week 31, Chile experienced an increase in A(H3N2) virus detections.

In Asia, local outbreaks of A(H3N2) viruses continued from southern mainland China with sporadic detections of A(H1N1)pdm09, A(H3N2) and influenza B viruses reported from some other countries.

Influenza activity remained low in Europe and North America.

Since August 2011 until 10 August 2012, the United States of America reported 154 laboratory confirmed human cases of variant influenza A(H3N2) virus (A(H3N2)v). All viruses tested so far are antigenically similar to the candidate vaccine viruses developed from earlier variant viruses, A/Minnesota/11/2010 X-203 and A/Indiana/10/2011 X-213, sensitive to oseltamivir and zanamivir, but resistant to admantine. All 154 A(H3N2)v viruses contain 7 gene segments from triple A(H3N2) North American swine viruses and the M gene from the A(H1N1)pdm09. Epidemiologically, most cases had direct or indirect exposure to swine. Clinically these cases are indistinguishable from seasonal influenza infection with no reports of severe disease. WHO GISRS laboratories have been alerted and provided with specific PCR protocols developed by the WHO CC in CDC Atlanta.

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