<prompt> Influenza virus causes new epidemic by 3-5 yrs -Antigenic driftAntigenic shiftCyclic trendsMosaicsm  <response>: Antigenic variations in Influenza Antigenic shift Antigenic drift Occurs due to Genetic recombinationreassoment Rearrangement Point mutation Nature Sudden Gradual insidious May lead to Epidemics pandemics Sporadic cases Ref: Park 25th edition Pgno : 166-172 