Influenza virus activity in the world

3 August 2012

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

Based on FluNet reporting (as of 31 July 2012, 12:10 UTC), during weeks 28 to 29 (8 to 21 July 2012), National Influenza Centres (NICs) and other national influenza laboratories from 60 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 11 524 specimens. 2 591 were positive for influenza viruses, of which 2001 (77.2%) were typed as influenza A and 590 (22.8%) as influenza B. Of the sub-typed influenza A viruses, 209 (11.4%) were influenza A(H1N1)pdm09 and 1 624 (88.6%) were influenza A(H3N2). Of the characterized B viruses, 32 (64%) belong to the B-Yamagata lineage and 18 (36%) to the B-Victoria lineage.


During weeks 28 and 29, influenza activity continued to increase in the southern hemisphere. Influenza A(H3N2) remained the predominant virus globally followed by influenza B and A(H1N1)pdm09 viruses.

Influenza A(H3N2) was the predominant virus subtype circulating in Australia and New Zealand. In New Zealand influenza activity increased while it decreased slightly in Australia compared to previous weeks. Local outbreaks of influenza B virus were reported in New Caledonia.

Varying levels of influenza activity have been reported from the African region. Ghana, and South Africa continued to report local outbreaks of A(H3N2) and influenza B viruses. The number of influenza B viruses detected in Madagascar increased while the A(H3N2) viruses decreased. Sporadic influenza activity was reported elsewhere in the region, including low level detections of A(H1N1)pdm09 viruses in several countries

A decreasing trend in influenza activity has been reported from Central and South America. Mixed circulation of influenza viruses continue to be reported. Influenza B viruses have predominated in Cuba and Ecuador while A(H1N1)pdm09 viruses were detected in the Plurinational State of Bolivia and Brazil. The number of A(H3N2) virus detected in Chile has decreased compared to previous weeks.

In Asia, influenza A(H3N2) activity increased in southern mainland China while influenza activity remained low in Europe and North America.

Other analyses