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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 2, 2010, 5:00 PM ET

This report provides an update to the international flu situation using data collected through June 27, 2010, and reported by the World Health Organization (WHO) on July 2.

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 continues to actively circulate in certain areas of the tropics, including the Caribbean, West Africa, and South and Southeast Asia. In the Southern Hemisphere, influenza A (H3N2) viruses are currently co-circulating with 2009 H1N1. In the Northern Hemisphere, the number of influenza B viruses detected has exceeded reports of influenza A.

Influenza A (H3N2) activity is currently increasing in Nicaragua and circulating at low levels in South Africa, Australia, East Africa, and South America. Low levels of 2009 H1N1 influenza activity have been reported from Chile and Argentina. 2009 H1N1 activity continues to increase in Southern regions of India and is circulating at low levels in several countries in Southeast Asia. Influenza type B continues to actively circulate in Central and Southern regions of Africa and is currently co-circulating with 2009 H1N1 in Bangladesh.


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 (69.7% of all influenza detections) and the Russian Federation (86.7%).
  • The proportion of influenza A (H3N2) detections increased in Australia and South Africa, while 2009 H1N1 is circulating as the predominant virus in Brazil and Chile. 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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