Interval between primary and secondary case is called as:-

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.