<prompt> All are true about Antigen drift except -It causes pandemicOccurs due to mutationOccurs frequentlyMinor antigenic changes  <response>: Antigenic drift the gradual sequential change in antigenic structure occuring regularly at frequent intervals. Antigenic drift is due to mutation and selection .It accounts for the periodic epidemics of influenza. REF:ANANTHANARAYAN AND PANIKERS TEXTBOOK OF MICROBIOLOGY 9TH EDITION PAGE NO-499 