Abstract
Pandemic, zoonotic and seasonal influenza viruses remain a threat to humans, and have major health and economic impacts globally. The pandemic threat due to Influenza A (H5N1) still exists since the virus is still endemic in poultry population in some countries. Sporadic cases of influenza A (H5N1) in humans are regularly reported. Efforts made by the animal sector to reduce circulation in poultry have contributed in reducing the risk of human H5N1 infection in many parts of the world. On 25 April 2009, Mexico, under the International Health Regulations (2005), notified the World Health Organization (WHO) about an outbreak of new influenza virus, which was characterized as a H1N1 virus previously not found in human. In less than nine weeks, the pandemic virus spread in the six WHO regions. On 11 June 2009, WHO announced a phase 6 pandemic alert. Thanks to the preparedness efforts carried out in a large number of countries in the world in response to influenza A (H5N1) threats, the international community has responded quite well to the pandemic. In particular, countries have been especially collaborative regarding the exchange of information and the global approach of access to supplies such as vaccine and antiviral drugs. The current pandemic presents significant differences to seasonal influenza epidemics and specific challenges are identified. (C) 2010 World Health Organization. All rights reserved.