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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

March 26, 2010, 5:30 PM ET

This report provides an update to the international flu situation using data collected through March 21, 2010, and reported by the World Health Organization (WHO) on March 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. 

Overall, 2009 H1N1 activity is highest in certain areas of Southeast Asia, West Africa, and tropical regions of the Americas. An increase in 2009 H1N1 activity has been reported in recent weeks in Central America and the tropical regions of South America. In West Africa, limited data show that 2009 H1N1 activity continues and may not have peaked. Although the 2009 H1N1 virus continues to be the predominant influenza virus circulating worldwide, seasonal influenza B viruses predominate in East Asia, and are circulating at low levels across Southeast and Western Asia, Eastern Africa, and in parts of Europe. In the temperate areas of the Southern Hemisphere, 2009 H1N1 activity remains low.

Selected Highlights

  • According to WHO, the majority of 2009 H1N1 virus isolates tested worldwide remain sensitive to oseltamivir, an antiviral medicine used to treat flu. Among 2009 H1N1 isolates tested worldwide, 267 have been found to be resistant to oseltamivir – 62 of these isolates were detected in the United States.
  • Influenza B continues to remain the predominating subtype in China, Mongolia and Iran, accounting for 81.6% of all influenza detections in China, 92.3% in Iran and 100% in Mongolia. Increased influenza B activity has also been observed in some European countries.
  • Sporadic influenza A (H3N2) activity has been reported from some countries in recent weeks, including Ghana and the Russian Federation.
  • 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.

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.

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