H1N1 Flu

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 05, 2010, 8:00 PM ET

Map of International Activity Estimates
(Including 2009 H1N1 Flu)

This report provides an update to the international situation as of January 31, 2010. The World Health Organization (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.
The 2009 H1N1 influenza virus continues to be the dominant influenza virus in circulation in the world. For the most recent period in which data are available, from January 17, 2009 to January 23, 2010, 54% were typed as influenza A and 46% as influenza B. Out of all subtyped influenza A viruses, 93% were 2009 H1N1 positive.
In temperate regions of the Southern Hemisphere, sporadic cases of 2009 H1N1 continue to be reported but no substantial increases in influenza activity have been observed. In the northern temperate and tropical regions of the Americas, 2009 H1N1 activity continues to decrease or remain low in most places. Influenza transmission continues to remain active in North Africa, certain areas of Eastern and Southeastern Europe, and parts of South and East Asia.

Selected Highlights

The 2009 H1N1 influenza virus is the predominant influenza virus in circulation worldwide.
According to WHO, the majority of 2009 H1N1 influenza isolates tested worldwide remain sensitive to oseltamivir, an antiviral medicine used to treat influenza disease. 225 2009 H1N1 isolates tested worldwide have been found to be resistant to oseltamivir – 59 of these isolates were detected in the United States.
China reported that, in recent weeks, 66% of all influenza-positive specimens were influenza B. Intermittent detections of seasonal A(H3N2) and influenza B viruses were also reported in parts of Africa, and East and Southeast Asia.

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

White House Report on 2009 H1N1 in the Southern Hemisphere
Issued August 2009 – This White House report was prepared by the Department of Health and Human Services (HHS) in coordination with the Office of the Director for National Intelligence (ODNI) and the Department of State (Dos) and describes the characteristics and impact of 2009 H1N1 influenza A virus in the Southern Hemisphere.
ECDC Interim Risk Assessment Influenza A (H1N1) 2009 Pandemic
Issued July 30, 2009 - This document provides an interim risk assessment of novel H1N1 flu in Europe prepared by ECDC.
World Health Organization Weekly Epidemiological record – Issued July 24, 2009
This document by WHO provides updates on the international novel H1N1 flu situation.
MMWR – Update: Novel Influenza A (H1N1) Virus Infection – Mexico, March-May, 2009 – Issued June 5, 2009 / Vol. 58 / No. 21.
This Morbidity and Mortality Weekly Report describes the novel influenza A (H1N1) outbreak in Mexico from March-May, 2009.
MMWR – Update: Novel Influenza A (H1N1) Virus Infections – Worldwide, May 6, 2009 – Issued May 8, 2009 / Vol. 58 / No. 17.
This Morbidity and Mortality Weekly Report describes worldwide novel influenza A (H1N1) infections as of May 6, 2009.