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
The time interval between the primary and secondary case is : 
Select and explain. 
A. Serial interval, B. Generation time, C. Median Incubation period, D. Secondary attack rate
A: Serial interval
Answer: A: Serial interval 
Explanation: Ans. is 'a' i.e. Serial interval Serial intervalThe gap in time between the onset of the primary case and the secondary case is called the serial interval.Generation time is the interval of time between receipt of infection by a host and maximal infectivity of that host.Median incubation periodis the time required for 50 percent of the cases to occur following exposure.