Abrupt ,drastic change in influenza is due to -

Abrupt ,drastic change in influenza is due to-Major abrupt drastic discontinuous changes in genome due to gene reassoment known as Antigenic shift. Antigenic shift Major abrupt drastic discontinuous changes in genome due to gene reassoment. 1. Responsible for Pandemic and major epidemic. 2. Occurs every 10-20 years. 1. Most common seen in Type A. 2. Results in a new strain is not related to predecessor strain. Antigenic drift Minor gradual sequential antigenic changes in genome due to point mutation. 1. Responsible for periodic Epidemic and sporadic cases. 2. Occurs every 2-3 years. 1. Seen in Type A, B. 2. Results in a different strain is related to predecessor strain. Virulence depends upon strains after genetic reassoment. Virulence -H5N1 >H1N1.