Antigenic variation is seen in all, EXCEPT:

Antigenic variability is highest in influenza virus type A and less in type B, while it has not been demonstrated in type C. The antigenic propeies of influenza viruses are determined by both hemagglutinin and neuraminidase. Antigenic variations are of two types: antigenic drift and antigenic shift. Antigenic drift is the gradual sequential change in antigenic structure occurring regularly at frequent intervals. It accounts for the periodical epidemics of influenza. Antigenic shift is an abrupt, drastic, discontinuous variation in the antigenic structure, resulting in a novel virus strain unrelated antigenically to predecessor strains.