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

March 12, 2010, 5:30 PM ET

Map of International Activity Estimates
(Including 2009 H1N1 Flu)

This report provides an update to the international situation using data collected through March 7, 2010, and reported by the World Health Organization (WHO) on March 12. 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.

In nearly all countries of the world where influenza infection is reported, the 2009 H1N1 influenza virus continues to predominate among all subtyped influenza A viruses. Based on FluNet data collected by 28 countries from February 21 to February 27, 2010, 92.8% of all subtyped influenza A viruses were 2009 H1N1 positive. Among specimens that tested positive for influenza, 69.2% were typed as influenza A and 30.8% as influenza B.

The 2009 H1N1 virus is currently most actively being transmitted in Southeast Asia. Limited data suggests increases in 2009 H1N1 activity in West Africa. Influenza B viruses are the predominant virus subtype in some countries in Asia and appear to be increasing in other parts of the world, too. 2009 H1N1 activity remains low in the Americas and in the temperate zone of the Southern Hemisphere.

Selected Highlights

According to WHO, the majority of 2009 H1N1 influenza isolates tested worldwide remain sensitive to oseltamivir, an antiviral medicine used to treat influenza disease. Among 2009 H1N1 isolates tested worldwide, 264 have been found to be resistant to oseltamivir – 61 of these isolates were detected in the United States.
Hong Kong SAR China reported that influenza B accounted for 63.5% of all influenza detections in the past reporting week. Influenza B is also the predominant subtype in China, and it is increasing in Iran, Mongolia, and the Russian Federation. Influenza A (H3N2) activity has been reported in some countries.
An influenza A (H1N1) virus of swine origin distinct from the 2009 H1N1 pandemic virus was recently found in three patients in Saskatchewan, Canada. The patients worked together at a hog operation and no further transmission has been documented.
As of February 18, 2010, WHO has 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.

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.