Simulating transmission scenarios of the Delta variant of SARS-CoV-2 in Australia

TL;DR

This study used an agent-based model to simulate the spread of the Delta variant of SARS-CoV-2 in Australia, evaluating intervention strategies and predicting epidemic peaks and healthcare impacts.

Contribution

It introduces a calibrated agent-based model to assess non-pharmaceutical interventions and vaccination effects on the Delta outbreak in Australia.

Findings

Inadequate control with current interaction reductions.

70% stay-at-home compliance could delay cases by 45 days.

Vaccination and social distancing predicted to peak mid-October 2021.

Abstract

An outbreak of the Delta (B.1.617.2) variant of SARS-CoV-2 that began around mid-June 2021 in Sydney, Australia, quickly developed into a nation-wide epidemic. The ongoing epidemic is of major concern as the Delta variant is more infectious than previous variants that circulated in Australia in 2020. Using a re-calibrated agent-based model, we explored a feasible range of non-pharmaceutical interventions, including case isolation, home quarantine, school closures, and stay-at-home restrictions (i.e., "social distancing"). Our modelling indicated that the levels of reduced interactions in workplaces and across communities attained in Sydney and other parts of the nation were inadequate for controlling the outbreak. A counter-factual analysis suggested that if 70% of the population followed tight stay-at-home restrictions, then at least 45 days would have been needed for new daily cases to fall from their peak to below ten per day. Our model predicted that, under a progressive vaccination rollout, if 40-50% of the Australian population follow stay-at-home restrictions, the incidence will peak by mid-October 2021: the peak in incidence across the nation was indeed observed in mid-October. We also quantified an expected burden on the healthcare system and potential fatalities across Australia.