<p>We evaluate the risk of yellow fever outbreaks in a major trade event, with a case study of Canton Fair (Guangzhou, China), caused by case importation at different stages of the trade event. Our baseline model is a standard vector-borne disease transmission dynamics system, but we incorporate the division of a calendar year into favorable and unfavorable seasons based on impacts of different climatic conditions (temperature in particular) on mosquito population dynamics. We also incorporate square-waves to describe scenarios of case importation. We then use this periodic switching model to inform the potential of outbreaks and intensity of outbreaks due to case importation in different periods in relation to the two seasons. Our results show that importation of cases (even with a single case introduced) in the favorable season can induce a large outbreak in the local population in the host city, and the intensity of outbreak depends on the total number of imported cases (up to a level, when local transmission dominates). We also incorporate the public health interventions-isolation and emergency vaccination-to the model to provide quantitative information for the event organizer and public health decision makers for the preparedness and rapid response to the outbreak induced by case importation.</p>