Epidemiology of transmissible diseases after elimination

Elimination of an infectious disease is often understood to mean the total absence of cases in a population. This situation can occur only if the enti re population is immune as a result of either natural disease or vaccinatio n. However, this costly and unrealistic scenario is not necessary to ensure elimination. more appropriately defined as a situation in which sustained transmission cannot occur and secondary spread from importations of disease will end naturally, without intervention. The authors describe the size an d duration of outbreaks caused by imported infections after indigenous tran smission has been eliminated. They show that the status of the elimination process can be monitored by assessing the proportion of cases imported and the distribution of outbreak sizes; Measles in Canada, the United States, a nd the United Kingdom provides a good example of the:relevance of these cri teria. Surveillance of the size and duration of these outbreaks enables mai ntenance of elimination to be monitored.