influenza viruses of the type A, including those causing seasonal epidemics of human influenza, are genetically labile and well adapted to elude host defenses. The tendency of influenza viruses to undergo frequent and permanent antigenic changes necessitates constant monitoring of the global influenza situation and annual adjustments in the composition of influenza vaccines. Due to this tendency of mutation, avian influenza mixed with a human flu, and was thus able to infect humans through direct contact with birds.

According to the World Health Organization, of the 115 people in four Asian countries who have been infected with H5N1 from late 2003 through 2005, 59 have died. Vaccines are the principal medical intervention for protecting individuals against pandemic influenza. If available rapidly and in sufficient quantities, they can reduce the morbidity and mortality in pandemic situations.

According to a news posted on Sept 28, 2005, government scientists at the US National Institute of Allergy and Infectious Diseases (NIAID) announced results from initial clinical trials of a vaccine being developed to protect humans against infection with H5N1 avian influenza. NIAID and MedImmune have joined forces to develop potential pandemic influenza vaccines. HHS Secretary Mike Leavitt today announced that NIAID and MedImmune Inc. have signed a cooperative research and development agreement for the development of vaccines against avian influenza viruses that have the potential to cause pandemics. Speaking of pandemic flu as an urgent health challenge, HHS