This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: DNB 2018, Subject name: Social & Preventive Medicine
Interval between primary and secondary case is called as:- 
Select and explain. 
A. Serial interval, B. Generation time, C. Incubation period, D. Lead time
A: Serial interval
Answer: A: Serial interval 
Explanation: The gap in time between the onset of the primary case and the secondary case is called "serial interval". Incubation period: The time interval between invasion by an infectious agent and appearance of the first sign or symptom of the disease in question. Generation time: interval of time between the receipt of infection by a host and maximal infectivity of that host Lead time: it is the advantage gained by screening, i.e. the period between diagnosis by early detection and diagnosis by other means.