text: how long have specific strains of flu been tracked as diligently as the current h5n1?   actually h5n1 is an older strain.  the strains have been tracked since the ability to recognize the specific types.   "influenza a subtypes are defined by the expression of two key surface proteins: hemagglutinin (h) and neuraminidase (n). sixteen hemagglutinins are known to exist, each of which can be “paired” with one of nine neuraminidase proteins. these influenza a subtypes are all maintained in aquatic birds, which serve as a continual source of new viruses. " older strains have only recently been tracked as a specific hn subtype.  the h5n1 first appeared in the literature in 1985.