This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: NEET 2019, Subject name: Microbiology
[{'content': 'Which vaccine strain is changed every yearly? \nSelect and explain. \nA. Influenza, B. Rabies, C. Hepatitis, D. Ebola', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Influenza a and b are the segmented viruses which contain 8 segments of nucleic acid. There is gradual sequential change in antigenic structure occurring regularly at frequent intervals which is known as antigenic drift. This antigenic drift is due to mediation and selection so their vaccine strain is changed every year.', 'role': 'assistant'}]