influenza a virus subtype h1n1 influenza a virus subtype h1n1 in virology, influenza a virus subtype h1n1 (a/h1n1) is a subtype of influenza a virus. major outbreaks of h1n1 strains in humans include the 1918 spanish flu pandemic, the 1977 russian flu pandemic and the 2009 swine flu pandemic. it is an orthomyxovirus that contains the glycoproteins hemagglutinin (h) and neuraminidase (n), antigens whose subtypes are used to classify the strains of the virus as h1n1, h1n2 etc. hemagglutinin causes red blood cells to clump together and binds the virus to the infected cell. neuraminidase is a type of glycoside hydrolase enzyme which helps to move the virus particles through the infected cell and assist in budding from the host cells. for the h1n1/09 virus strain responsible for the 2009 flu pandemic, see pandemic h1n1/09 virus. for the 1918 influenza a (h1n1) pandemic, see spanish flu. influenza a virus subtype h1n1 virus classification (unranked): virus realm: riboviria kingdom: orthornavirae phylum: negarnaviricota class: insthoviricetes order: articulavirales family: orthomyxoviridae genus: alphainfluenzavirus species: influenza a virus serotype: influenza a virus subtype h1n1 strains pandemic h1n1/09 virus 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