historical annual reformulations of the influenza vaccine historical annual reformulations of the influenza vaccine since 1999, the world health organization (who) has issued annual recommendations for influenza vaccine formulations. one reformulation of the influenza vaccine is for the northern hemisphere, and the other is for the southern hemisphere. both recommendations are trivalent, i.e. featuring three strains. influenza (flu) types avian a/h5n1 subtype canine equine swine a/h1n1 subtype vaccines 2009 pandemic pandemrix live attenuated seasonal flu vaccine brands treatment amantadine baloxavir marboxil laninamivir oseltamivir peramivir rimantadine umifenovir zanamivir pandemics 1889-1890 russian flu 1918 spanish flu 1957-1958 asian flu 1968 hong kong flu 1977 russian flu 2009 swine flu outbreaks 1976 swine flu 2006 h5n1 india 2007 australian equine 2007 bernard matthews h5n1 2008 west bengal 2015 united states h5n2 outbreak 2020–2022 h5n8 outbreak