We calculate the probability distribution of D, the total delay until an epidemic gathers momentum by noting that it is given by D = D 1 +D 2 , where D 1 is the time until an epidemic is first initiated and D 2 is the time from initiation until the local epidemic gathers momentum. For an epidemic to be first initiated in the at-risk country on day d, it must have not been initiated on all previous days. Hence the probability distribution of the time delay (D 1 ) until the epidemic is first initiated in the at-risk country following identification in the source region is described by: