Predicting localised measles outbreak potential in Australia

Abstract

IntroductionAustralia has achieved measles elimination as announced in March 2014 by the WHO Western Pacific Regional Committee, based on several lines of evidence. However, despite strong national evidence for elimination, there remains substantial regional variation in vaccine coverage, has resulted in recent outbreaks and potential for increased frequency in the future. MethodsIn this study, we apply a multiple cohort model of measles immunity, stratified by age and local geographic area to predict trends in the measles reproduction number R. In addition, we use branching process models of outbreak risks to predict state-level probabilities of the occurrence of measles outbreaks over the next 20 years. ResultsOur results suggest increasing risks of large measles outbreaks over this period, in particular in the states of Queensland and New South Wales. In addition, there is wide variation in predicted R values by smaller geographic areas, although uncertainty in age-specific immunity limits the precision of our results. DiscussionOur predictions align with observed outbreaks in Australian states and suggest our approach to determining future outbreak risks could be applied more widely in elimination or near-elimination settings.