Public health measures for the prevention of community spread of influenza viruses are of limited effectiveness.  Influenza vaccines are estimated to be 70-80% effective in either preventing influenza infection or at least reducing the severity of an influenza infection if the viral antigens in the vaccine are similar to the prevalent circulating virus.  A decision to develop a global influenza vaccine program requires: (1) detection and laboratory confirmation of a “new” influenza virus; and (2) some indication that this new virus is spreading rapidly in human populations.  The time from recognition of a new influenza virus and documentation of its spread takes at least a few months, and then the time required to develop and make millions of doses of a new flu vaccine also requires a few more months.  The decision to develop a global flu vaccine program for the 2009 H1N1 virus was made as rapidly as possible but still sufficient supplies of the 2009 flu vaccine were not available until the flu season was over in the Sothern hemisphere and had peaked or was peaking in the Northern hemisphere.