H1N1 is a subtype of Influenza A virus, not a unique entity.
H and N indicate surface proteins hemagglutinin 1 and neuraminidase 1, respectively.

H1N1 is the subtype to which the viruses of Spanish Flu and Swine Flu belong, but there are many members of this subtype; they are not the same. The specific virus causing the present outbreak is unique and new; it differs from others of the same subtype, some of which are virulent and some of which do not cause any serious problems in humans.

Several articles on this may be found through google.