2009 H1N1 Flu: International Situation Update

This report provides an update to the international flu situation using data collected through March 28, 2010, and reported by the World Health Organization (WHO) on April 1. WHO continues to report laboratory-confirmed 2009 H1N1 flu cases and deathsExternal Web Site Icon 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.

Currently, 2009 H1N1 influenza activity is highest in the tropical regions of Asia, the Americas and Africa. In the temperate areas of the Northern and Southern Hemisphere, 2009 H1N1 influenza virus continues to circulate at low levels. Although the 2009 H1N1 virus continues to be the predominant influenza virus circulating worldwide, influenza B viruses are predominant in most of East Asia and have been detected at low levels across Southeast and Western Asia, East Africa, and parts of Eastern and Northern Europe. Seasonal influenza A viruses are still being detected in parts of Asia and Australia.


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, 268 have been found to be resistant to oseltamivir – 64 of these isolates were detected in the United States.
* Influenza B remains the predominant flu strain in East Asia, accounting for 66.7% of all influenza viruses reported in the Republic of Korea, 71.6% in the Russian Federation, 84.2% in China, and 100% in Mongolia and Iran. An increase in influenza B activity has also been reported in some European countries.
* Seasonal influenza A activity has been reported recently in some countries in recent weeks, including China, Ghana and Thailand.
* 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:

o an A/California/7/2009 (H1N1)-like virus;
o an A/Perth/16/2009 (H3N2)-like virus*;
o 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.