The continual genetic change that is introduced into the influenza genome is called antigenic:

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Antigenic drift refers to the slow genetic changes that occur in the virus over time, resulting in minor variations in the surface antigens. This can result in the need for updated versions of the influenza vaccine each year to keep up with these changes. Antigenic shift, on the other hand, refers to major changes that occur when two or more different strains of the virus combine to create a new strain with a novel antigen profile.

The Continual Genetic Change That Is Introduced into the Influenza