This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
[{'content': 'Influenza virus causes new epidemic by (3-5 yrs) - \nSelect and explain. \nA. Antigenic drift, B. Antigenic shift, C. Cyclic trends, D. Mosaicsm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Antigenic variations in Influenza Antigenic shift Antigenic drift Occurs due to Genetic recombination/reassoment / Rearrangement Point mutation Nature Sudden Gradual / insidious May lead to Epidemics/ pandemics Sporadic cases Ref: Park 25th edition Pgno : 166-172', 'role': 'assistant'}]