Antigenic shift -
Antigenic shift is an abrupt, drastic, discontinuous variation in the antigenic structure resulting in a novel virus strain unrelated antigenically to predecessor strain. REF: Anantha Narayan AND PANIKER'S TEXTBOOK OF MICROBIOLOGY 9TH EDITION PAGE NO:499
Occurs every 2-3 years
Gradual change over time
Results from genetic recombination
Occurs in all influenza viruses
Virology