Influenza virus activity in the world
17 February 2012
Based on FluNet reporting (as of 14 February 2012, 12:35 UTC) during weeks 4 to 5 (22 January 2012 to 4 February 2012), National Influenza Centres (NICs) and other national influenza laboratories from 85 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 41423 specimens. 7382 were positive for influenza viruses, of which 5693 (77.1%) were typed as influenza A and 1689 (22.9%) as influenza B. Of the sub-typed influenza A viruses, 995 (23%) were influenza A(H1N1)pdm09 and 3327 (76.9%) were influenza A(H3N2). Of the characterized B viruses, 106 (33%) belong to the B-Yamagata lineage and 215 (67%) to the B-Victoria lineage.
During weeks 4 and 5 in 2012, laboratory confirmed influenza activity increased in many countries in the northern hemisphere with localized to widespread activity occurring.
Globally influenza A(H3N2) continued to be the predominant virus subtype detected. In general, influenza A(H1N1)pdm09 and B activity was low, except in Mexico where A(H1N1)pdm09 remained the predominant virus and some Asian countries where influenza B continued to be the main circulating virus type. The overall proportion of two B lineage viruses remained the same as reported for the previous fortnight, with approximately two thirds being B-Victoria and one third B-Yamagata viruses.
In Europe, the Middle East, North Africa and North America, influenza A(H3N2) activity increased in many countries. Influenza B virus was detected at low levels with A(H1N1)pdm09 detected only sporadically.
In Asia, influenza activity of A(H3N2) and B viruses continued to increase, with B viruses predominating in China and China Hong Kong Special Administrative Region, and A(H3N2) viruses in Japan, Republic of Korea and a number of other countries. Influenza A(H1N1)pdm09 was detected at low levels.
In the southern hemisphere, influenza activity remained low with the majority of the sporadic virus detection identified as influenza A(H3N2).
As reported in the last summary, the influenza A(H5N1) virus from a recent human case in China, belonging to clade 22.214.171.124, was shown to be sensitive to NAIs and adamantanes . Antigenically it reacted well with post-infection antiserum to the vaccine candidate virus A/Anhui/1/2005. An A(H5N1) virus was detected in late January from a human case in Viet Nam who subsequently died. The virus is undergoing further genetic and antigenic characterization.