This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Virology, Subject name: Microbiology
[{'content': 'Antigenic drift and antigenic shift is seen in \nSelect and explain. \nA. Swine flu virus, B. Influenza A virus, C. Rota virus, D. Herpes virus', 'role': 'user'}, {'content': "Answer: B \nExplanation: ANTIGENIC DRIFT It is a minor change occuring due to point mutations in the HA/NA gene ,resulting in alteration of amino acid sequence of the antigenic sites on HA/NA , such that virus can escape recognition by the host's inmune system. Seen in both influenza type A and B More frequent- every 2-3 years ANTIGENIC SHIFT It is an abrupt , major drastic , discontinuous variation in the sequence of a viral surface protein , that occurs due to genetic reassoment between genomes of 2 or more influenza viruses infecting the same host cells , resulting in a new virus strain, unrelated anti genetically to the predecessor strains Occurs only in influenza type A Less frequent - every 10 -20 yrs Ref : essentials of Medical microbiology apurba sastry 1st edition page 459", 'role': 'assistant'}]