Influenza virus activity in the world
8 June 2012
Based on FluNet reporting (as of 5 June 2012, 11:50 UTC), during weeks 20 to 21 (13 May 2012 to 26 May 2012), National Influenza Centres (NICs) and other national influenza laboratories from 82 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 19 710 specimens. 2 297 were positive for influenza viruses, of which 1 699 (74%) were typed as influenza A and 598 (26%) as influenza B. Of the sub-typed influenza A viruses, 157 (10.6%) were influenza A(H1N1)pdm09 and 1 325 (89.4%) were influenza A(H3N2). Of the characterized B viruses, 19 (61.3%) belong to the B-Yamagata lineage and 12 (38.7%) to the B-Victoria lineage.
Summary
During weeks 20 and 21 in 2012, laboratory confirmed influenza activity was very low in both the northern and southern hemispheres with the exception of a few countries. Influenza A(H3N2) remained as the predominant virus subtype detected globally. Influenza B virus was dominant in a number of countries while influenza A(H1N1)pdm09 virus was detected in very low numbers.
In Asia, high influenza A(H3N2) virus activity, which is unusual at this time of year, was reported in the China Hong Kong Special Administrative Region. Influenza B was the main virus detected in India and the Republic of Korea but at lower levels than in recent weeks.
In Europe, the number of influenza virus detections continued to decline. In week 20, the overall proportion of influenza B virus detected was higher compared to that of influenza A, unlike earlier in the season where A(H3N2) viruses were dominant.
In North America, influenza B was the predominant virus circulating in both Canada and the United States of America with co-circulation of mainly A(H3N2).
In the Caribbean and Central America influenza virus activity was reported in the Dominican Republic and El Salvador where A(H3N2) and influenza A(H1N1)pdm09 virus were the main circulating virus subtypes respectively.
In the southern hemisphere, influenza activity remained low in general. Influenza A(H1N1)pdm09, A(H3N2) and B viruses were detected sporadically in Africa and Oceania. Madagascar reported local outbreaks of predominantly A(H3N2) virus, with several co-infections of influenza A and B virus detected. In South America, influenza A(H1N1)pdm09 and B viruses co-circulated in the Plurinational State of Bolivia while the predominant virus in Chile remained A(H3N2). Both A(H1N1)pdm09 and A(H3N2) virus subtypes were reported at low levels in Brazil.
