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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

July 19, 2010, 5:00 PM ET

This report provides an update to the international flu situation using data collected through July 12, 2010, and reported by the World Health Organization (WHO) on July 16.

WHO continues to report laboratory-confirmed 2009 H1N1 flu deaths on its Web page. These fatal cases are an under-representation of the actual numbers, as many deaths are never tested or recognized as flu related.
2009 H1N1 viruses and seasonal influenza A (H3N2) viruses are being detected in the tropical regions, including Asia and the Americas. In the Southern Hemisphere, respiratory disease activity has been low, with the exception of South Africa. In the Northern Hemisphere, influenza detections have been limited.

In late June and early July, South Africa reported an increase in influenza B and influenza A (H3N2) virus activity. In June, there was a resurgence of 2009 H1N1 activity in Ghana. Influenza activity has been low to sporadic in Argentina and Chile, and influenza like illness (ILI) activity has been low in Australia and New Zealand. One region in southern India has reported active transmission of 2009 H1N1 virus. Some seasonal B influenza viruses are being found in China, though ILI levels are similar to those reported in previous years.  2009 H1N1 is actively circulating in Colombia and Costa Rica, although generally at low levels. 

Selected Highlights

  • According to WHO, the majority of 2009 H1N1 virus isolates tested worldwide remains sensitive to oseltamivir, an antiviral medicine used to treat flu. Among 2009 H1N1 isolates tested worldwide, 298 have been found to be resistant to oseltamivir – as of May 28, 2010, 67 of these isolates were detected in the United States. Approximately 1% of U.S. 2009 H1N1 viruses tested by CDC since September 1, 2009, have been resistant to oseltamivir.
  • Influenza B continues to predominate in many countries of the Northern Hemisphere, including China (56.9% of all influenza detections).
  • In Australia, there were far more 2009 H1N1 detections (88.9% of detections) than A (H3N2) (11.1% of detections).
  • On February 18, 2010, WHO 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 a 2010 Southern Hemisphere vaccine virus.

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.

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