Causes of antigenic drift in influenza viral infections -: (A) Small mutation in neuraminidase and hemagglutinin, (B) Large mutations in viral genome, (C) Step mutations in viral genome, (D) None of the above
Answer is A. Antigenic drift is due to mutation and selection. REF:ANANTHANARAYAN AND PANIKER'S TEXTBOOK OF MICROBIOLOGY 9TH EDITION PAGE NO-499