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.

Novel H1N1 Flu: International Situation Update

July 31, 2009, 11:00 AM ET

Map of International Activity Estimates
(Including Novel H1N1)

This situation report provides an update of the international situation as of July 28, 2009. As of July 27, WHO regions have reported 134,503 laboratory-confirmed cases of novel influenza A (H1N1) and 816 deaths. The lab-confirmed cases represent an underestimation of total cases in the world as many countries have shifted to strategies of clinical confirmation and prioritization of laboratory testing for only persons with severe illness and/or high risk conditions. Currently, the novel influenza A (H1N1) virus is the dominant influenza virus in circulation in New Zealand, Australia, Chile, Argentina and Brazil. Influenza viruses currently being detected in England and Canada are almost exclusively novel Influenza A (H1N1). Following a seasonal influenza season that was dominated by influenza A (H3N2) virus circulation, South Africa is now detecting novel influenza A (H1N1) through its routine surveillance system. However, currently influenza A (H3N2) remains the dominant virus in circulation in South Africa. Many seasonal influenza viruses from these countries have not been subtyped. Of those that have been subtyped in Australia, South Africa, and Argentina, the majority are influenza A (H3N2) viruses.

Selected Highlights

Novel influenza A (H1N1) continues to circulate widely.
Descriptive epidemiology of cases remains similar across countries.
Isolates sequenced at WHO and CDC suggest that circulating novel influenza A (H1N1) viruses look similar to A/California/07/2009 (the reference virus selected by WHO as a potential candidate for novel influenza A (H1N1) vaccine).

International Resources for Novel H1N1 Information

Health Organizations

World Health Organization (WHO) Regional Offices

Travel and Novel H1N1 Flu

Human cases of novel H1N1 flu virus infection have been identified in the United States and several countries around the world. For information on novel H1N1 flu and travel, see the CDC H1N1 Flu and Travel website.

Reports and Publications

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.