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': 'False about antigen drift? \nSelect and explain. \nA. Causes pandemic, B. Occurs due to mutation, C. Occurs more frequently, D. Affected by previous antibodies', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Causes pandemic o Antigenic shift (not drift) is responsible for pandemic. o Antigenic drift occurs due to point mutation. o Antigenic drift occurs more frequently (2-3 years) than antigenic shift (10-15 years). o Antigenic drift is influenced by the presence of antibodies to the predecessor strains in the host population.", 'role': 'assistant'}]