This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infectious Disease Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Serial interval is - \nSelect and explain. \nA. Interval between primary and secondary case, B. Interval between first case and last case, C. Interval between infection to maximum infectivis, D. Interval between incubation period and gestational period', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Interval between primary and secondary case Serial intervalo The gap time between onset of primary case and secondary case.o By collecting information about a whole series of such onset, we get a distribution of secondary cases from which we can guess the incubation period.", 'role': 'assistant'}]