The effects of size of spillover event on the likelihood of observing an outbreak. Probability that no major outbreak unfolds as a function of the initial number of infectious cases introduced into the population. Epidemiological parameter values for EVD are shown in Table 1. The mean time from symptoms onset to diagnosis (γ
a0) is set at three days. The isolation effectiveness is set at 0 (that is, l
0. =1). Population size N is set at 100,000. The baseline value of R0 is set at 1.8. The curve corresponds to the mean of the results obtained from 500 model simulations. EVD, Ebola virus disease; R0, basic reproduction number.