This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': 'Not true regarding influenza virus is -a) All types exhibit antigenic shiftb) Only type A shows antigenic driftc) Drift is accumulation of point mutationsd) None of the above \nSelect and explain. \nA. ac, B. a, C. ab, D. bc', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Antigenic shift is seen only in Influenza \'A\' virus.\nAntigenic drift is seen in Influenza A and B.\nAntigenic drift involves "point mutation" in the gene owing to selection pressure by immunity in the host population.\nInfluenza shows cyclic trend due to these antigenic variations\nType A epidemics every 2-3 years\nType B epidemics every 4-7 years\nType A pandemics every 10-15 years', 'role': 'assistant'}]