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': 'Causes of antigenic drift in influenza viral infections: \nSelect and explain. \nA. Small mutations in neuraminidase and hemagglutinin, B. Large mutations in hemagglutinin only, C. Step mutations in viral genome, D. None of the above', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Small mutations in neuraminidase and hemagglutinin Antigenic drift: The gradual, sequential, regular antigenic change in influenza virus is known as antigenic drift. This occurs due to minor antigenic changes due to point mutations in the HA or NA occurring at frequent intervals. This is caused even by a single mutation affecting HA glycoprotein. The antigenic drift is characterized by changes in certain epitopes in the HA, while others are being conserved.", 'role': 'assistant'}]