H1N1 describes the cell interaction characteristics. The ‘H’ helps the virus bind to cells before infection (hemagglutinin). The ‘N’ helps the virus release from the cell (neuraminidase). The species infected makes no difference as these (glycoproteins) remain the same. The H5N1 for instance has a different H configuration which is why it isn’t spread as readily in humans. The initial binding of the virus is less compatible.
I couldn’t do that again to those apostrophes if I tried...