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

October 09, 2009, 11:00 AM ET

Map of International Activity Estimates
(Including 2009 H1N1 Flu)

This report provides an update to the international situation as of October 2, 2009. As of October 2, 2009, the World Health Organization (WHO) regions have reported over 343,298 laboratory-confirmed cases of 2009 H1N1 with at least 4,108 deaths, which is an increase of at least 24,373 cases and 191 deaths since September 20. The laboratory-confirmed cases represent a substantial underestimation of total cases in the world, as many 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. From April 19 to September 19, 2009, 59.8% of influenza specimens reported to WHO were 2009 H1N1 viruses. In temperate regions of the Southern Hemisphere, disease due to 2009 H1N1 is declining or has returned to baseline. In tropical regions of the Americas and Asia, influenza activity due to 2009 H1N1 remains variable. In temperate regions of the Northern Hemisphere, there is increased influenza-like illness (ILI) activity due to 2009 H1N1 in many areas, including in most of the United States, parts of Mexico and Canada, some countries in Europe, and parts of Central and Western Asia.

Selected Highlights

The 2009 H1N1 influenza virus is the predominant influenza virus in circulation in most countries worldwide.
The epidemiology of disease caused by 2009 H1N1 influenza in the Southern Hemisphere is very similar to that described in the United States in the spring of 2009.
There have been no significant changes detected in the 2009 H1N1 influenza viruses isolated from persons in the Southern Hemisphere as compared to viruses isolated from persons in the Northern Hemisphere.
As of October 2, 2009, WHO reported that more than 10,000 2009 H1N1 influenza isolates worldwide were tested and found to be sensitive to oseltamivir, an antiviral medicine used to treat influenza disease. Only 28 2009 H1N1 isolates tested have been found to be resistant to oseltamivir – 11 of these isolates were detected in the United States.
On September 18, 2009, the United States, together with Australia, Brazil, France, Italy, New Zealand, Norway, Switzerland and the United Kingdom, announced plans to donate 2009 H1N1 vaccine to the developing world.

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.