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Influenza virus activity in the world

20 May 2011

Virological summary

During weeks 17 to 18 (24 April 2011 to 07 May 2011), in general, a steady decline in numbers of laboratory detections of influenza A(H1N1)2009, A(H3N2) and B viruses has been observed, with only a few countries reporting sporadic or local activity.

At low level, influenza B viruses continued to be predominant relative to influenza A viruses, particularly in Canada and parts of Asia and Europe. Influenza A(H1N1)2009 was the predominant virus in some countries in Central and South America. Influenza A(H3N2) was the most prevalent virus in a few countries such as Brazil, Democratic Republic of the Congo and Rwanda.

The vast majority of recently characterized viruses remain antigenically similar to the WHO recommended vaccines for the 2010-2011 northern hemisphere and 2011 southern hemisphere influenza seasons.

During weeks 17 to 18 National Influenza Centres (NICs) from 82 countries, areas or territories reported data to FluNet*. A total of 1,017 specimens were reported as positive for influenza viruses, 358 (35.2%) were typed as influenza A and 659 (64.8%) as influenza B. Of the sub-typed influenza A viruses, 54% were influenza A(H1N1)2009 and 46% were influenza A(H3N2).

(FluNet data as of 17 May 2011 13:30 UTC)

* Some NICs report to FluNet retrospectively leading to updates of previous summary data.

Influenza virus detection by type/subtype in countries, areas or territories:

• Influenza A(H1N1)2009: Australia, Cambodia, Canada, China, Costa Rica, Denmark, Dominican Republic, Ghana, Japan, Kenya, Mexico, Norway, Oman, Romania, Russian Federation, Slovakia, Slovenia, South Africa, Sri Lanka, Sweden, Thailand, Ukraine, United States of America, Venezuela, Viet Nam
• Influenza A(H1N1) (old seasonal virus): no report
• Influenza A(H3N2): Algeria, Argentina, Australia, Brazil, Canada, China, Cuba, Democratic Republic of the Congo, France, Ghana, Iran (Islamic Republic of), Japan, Madagascar, Mali, Russian Federation, Rwanda, Turkey, United States of America
• Influenza A(H5): no report
• Influenza B: Brazil, Bulgaria, Canada, China, Croatia, El Salvador, Estonia, France, Georgia, Germany, Ghana, Greece, Iceland, India, Iran (Islamic Republic of), Jamaica, Japan, Kenya, Latvia, Madagascar, Mali, Mexico, Norway, Oman, Poland, Romania, Russian Federation, Slovakia, Sri Lanka, Sweden, Switzerland, Thailand, Turkey, Ukraine, United Kingdom of Great Britain and Northern Ireland, United States of America, Viet Nam
• No influenza activity: Afghanistan, Armenia, Austria, Azerbaijan, Belarus, Belgium, Bosnia and Herzegovina, Cameroon, Colombia, Ecuador, Ethiopia, Finland, France, Honduras, Hungary, Italy, Kyrgyzstan, Lao People's Democratic Republic, Lithuania, Luxembourg, Malta, Mauritius, Mongolia, Morocco, Netherlands, Panama, Paraguay, Portugal, Senegal, Serbia, Slovakia, Spain, Switzerland, Togo, Tunisia, Turkey, United Republic of Tanzania