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Content on this page was developed during the 2009-2010 H1N1 pandemic and has not been updated.

  • The H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
  • The English language content on this website is being archived for historic and reference purposes only.
  • For current, updated information on seasonal flu, including information about H1N1, see the CDC Seasonal Flu website.

2009 H1N1 Flu: International Situation Update

February 26, 2010, 4:00 PM ET

This report provides an update to the international situation using data collected through February 21, 2010, and reported by the World Health Organization (WHO) on February 26. WHO continues to report laboratory-confirmed 2009 H1N1 flu cases and deaths on its Web page. These laboratory-confirmed cases represent a substantial underestimation of total cases in the world, as most countries focus surveillance and laboratory testing only on people with severe illness.

Based on FluNet data collected by 32 countries from February 6 - 13, 2010, 48.3% of specimens testing positive for influenza were typed as influenza A and 51.7% as influenza B. In nearly all countries of the world where influenza infection is reported, the 2009 H1N1 influenza virus continues to predominate among all subtyped influenza A viruses. Out of all subtyped influenza A viruses, 90% were 2009 H1N1 positive.

Little flu activity has been reported in the temperate regions of the Southern Hemisphere in 2010 to date. In the temperate regions of the Northern Hemisphere, the 2009 H1N1 influenza virus continues to be detected across many countries. However, influenza activity continues to decline or remain low in most countries. In the Americas, both in the tropical and northern temperate regions, 2009 H1N1 continues to circulate at low levels, but overall influenza activity continues to decline or remain low in most places. In tropical regions of Asia, several countries reported an increasing trend of influenza activity, but overall intensity remains low. The most active areas of influenza transmission are currently in parts of South and Southeast Asia and in certain areas of East and Southeastern Europe.

Selected Highlights

  • According to WHO, the majority of 2009 H1N1 influenza isolates tested worldwide remain sensitive to oseltamivir, an antiviral medicine used to treat influenza disease. Among 2009 H1N1 isolates tested worldwide, 253 have been found to be resistant to oseltamivir – 60 of these isolates were detected in the United States.
  • Influenza B activity continues to increase in China and Hong Kong Special Administrative Region (SAR) of China. Hong Kong SAR China has reported increased influenza B activity accounting for 56.1% of all influenza detections, while in China it accounted for 83.5%. In addition to the increasing proportion of influenza type B viruses detected in China, low levels of seasonal influenza A (H3N2) and type B viruses are circulating in parts of Africa and Asia.
  • As of February 18, 2010, WHO has published recommendations for the following viruses to be used for influenza vaccines in the 2010-2011 influenza season of the Northern Hemisphere:
    • an A/California/7/2009 (H1N1)-like virus;
    • an A/Perth/16/2009 (H3N2)-like virus*;
    • a B/Brisbane/60/2008-like virus.

* A/Wisconsin/15/2009 is an A/Perth/16/2009 (H3N2)-like virus and is
2010 Southern Hemisphere vaccine virus.

International Resources for 2009 H1N1 Information

Health Organizations

World Health Organization (WHO) Regional Offices

Travel and 2009 H1N1 Flu

Human cases of 2009 H1N1 flu virus infection have been identified in the United States and several countries around the world. For information on 2009 H1N1 flu and travel, see the CDC H1N1 Flu and Travel website.

Reports and Publications

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