<prompt> Not true regarding influenza virus is -All types exhibit antigenic shiftOnlybtype A shows antigenic driftDrift is accumulation of point mutationsNone of the above  <response>: Antigenic drift the gradual sequential change in antigenic structure occurring 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 