Modelling the impact of COVID-19 in Australia to inform transmission reducing measures and health system preparedness

Robert Moss; James Wood; Damien Brown; Freya Shearer; Andrew J Black; Allen Cheng; James M McCaw; Jodie McVernon

A case targeted public health intervention was simulated. Cases were isolated at the point of diagnosis (assumed 48 hours after symptom onset), limiting the effective infectious period and reducing infectiousness by 80%. Targeted quarantine of close contacts was implemented in the model framework by dynamic assignment of a transient 'contact' label. Each time a new infectious case appears in the model, a fixed number of temporary 'contacts' are labelled. Only contacts can progress through the exposed and infectious states, however the majority remain uninfected and return to their original 'non-contact' status within 72 hours. We assumed that 80% of identified contacts adhered to quarantine measures and that the overall infectiousness of truly exposed and infected contacts was halved by quarantine, given delayed and imperfect contact tracing and the risk of transmission to household members.