Influenza virus activity in the world
18 January 2013
Based on FluNet reporting (as of 15 January 2013, 16:20 UTC), during weeks 52 in 2012 and 1 in 2013 (23/12/2012 to 05/01/2013), National Influenza Centres (NICs) and other national influenza laboratories from 93 countries, areas or territories reported data. The WHO GISRS laboratories tested more than 45 880 specimens. 13 183 were positive for influenza viruses, of which 10 370 (78.7%) were typed as influenza A and 2 813 (21.3%) as influenza B. Of the sub-typed influenza A viruses, 727 (12.4%) were influenza A(H1N1)pdm09 and 5 129 (87.6%) were influenza A(H3N2). Of the characterized B viruses, 25 (92.6%) belong to the B-Yamagata lineage and 2 (7.4%) to the B-Victoria lineage.
During week 52 in 2012 and week 1 in 2013, influenza activity continued to increase in the northern hemisphere. Influenza activity remained sporadic in the southern hemisphere. All three circulating virus types have remained antigenically similar to the current 2012-2013 northern hemisphere influenza vaccine. No oseltamivir or zanamivir resistant viruses have been reported to date for the current season. Globally, A(H3N2) viruses remain the predominant subtype followed by influenza B and A(H1N1)pdm09 viruses but the latter is increasing in some countries compared to earlier in the season.
Influenza activity has remained high in the United States of America with 47 states reporting widespread influenza activity. A(H3N2) viruses remained the predominant circulating subtype followed by influenza B viruses. A(H1N1)pdm09 viruses have been detected sporadically. In Canada, widespread A(H3N2) influenza activity has been reported. The predominant virus in Mexico was influenza B with co-circulation of A(H3N2).
In contrast to North America, countries in northern and western Europe have reported increasing detections of A(H1N1)pdm09 viruses relative to A(H3N2) viruses in recent weeks. Influenza B also co-circulated and was the predominant virus type in some European countries.
In the Eastern Mediterranean region, influenza activity was variable. The Islamic Republic of Iran reported co-circulation of A(H1N1)pdm09 and influenza B viruses with the proportion of A(H1N1)pdm09 viruses increasing. Pakistan reported co-circulation of A(H3N2) and influenza B viruses. Jordan continued to report A(H1N1)pdm09 virus detections.
In Asia, influenza activity increased in northern China while activity remained low in southern China. Although A(H3N2) viruses were the predominant subtype reported in China, the proportion of A(H1N1)pdm09 virus detections have been increasing. Elsewhere in the region, Japan continued to report A(H3N2) viruses and the Republic of Korea reported increased A(H1N1)pdm09 and A(H3N2) virus detections. In central and south America, influenza activity has remained low. Sporadic detections of influenza B, A(H1N1)pdm09, A(H3N2) have been reported.
Sporadic detections of influenza B viruses have been reported from the African region, particularly in central and eastern Africa. Algeria reported the co-circulation of A(H1N1)pdm09, A(H3N2) and influenza B viruses.