True statement about influenza

1. Influenza virus is transmitted from person to person primarily in droplets released by sneezing and coughing. 2. Antigenic variations are a unique feature of influenza virus. The surface antigens HA and NA show variations and are primarily responsible for antigenic variations exhibited by influenza viruses. Antigenic variations are of two types: antigenic shift and antigenic drift. 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 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 Related to predecessor strain