Population-based analysis of the epidemiological features of COVID-19 epidemics in Victoria, Australia, January 2020 – March 2021, and their suppression through comprehensive control strategies

Abstract

Background Victoria experienced the greatest burden of COVID-19 in Australia in 2020. This report describes key epidemiological characteristics and corresponding control measures between 17 January 2020 and 26 March 2021. Methods COVID-19 notifications made to the State Government Department of Health were used in this analysis. Epidemiological features are described over 4 phases, including enhancements to testing, contact tracing and public health interventions. Demographic and clinical features of cases are described. Findings Victoria recorded 20,483 cases of COVID-19, of which 1073 (5•2%) were acquired overseas and 19,360 (95%) were locally acquired. The initial epidemic (Phase I) was well-contained through public health interventions and was followed by relaxation of restrictions and low-level community transmission (Phase II). However, an outbreak in a hotel used to quarantine returned travellers led to wide-scale community transmission accounting for a majority (91%) of cases (Phase III). Outbreaks occurred in vulnerable settings including aged care and hospitals, contributing to high hospitalisation (12%) and case fatality rates (3•7%). Aggressive restrictions ultimately led to local elimination, and subsequent outbreaks have been swiftly managed with improved processes (Phase IV). The demographic composition of cases evolved across phases from an older, wealthier population to a less advantaged younger population, with many from culturally and linguistically diverse backgrounds. Interpretation Over time, adaptations to the public health response have strengthened capacity to respond to new cases and outbreaks in a more effective manner. The Victorian experience underscores the importance of authentic engagement with diverse communities and balancing restrictions with livelihoods.

Area‐level social and economic factors and the local incidence of SARS‐CoV‐2 infections in Victoria during 2020

“…The first COVID‐19 wave in Victoria was linked with returned overseas travellers, the second wave with inadequate quarantining of returned overseas travellers in hotel quarantine in Melbourne. 3 Early outbreaks during the second wave were initially restricted to ten suburbs, subject to strict lockdown restrictions announced on 29 June 2020, 11 and nine housing towers in North Melbourne and Flemington (about 3000 residents), subject to lockdown from 9 July 2020. 12 These targeted containment measures were unsuccessful, and rapid transmission ensued across metropolitan Melbourne and, to a lesser extent, regional Victoria.…”

“…The relatively small first wave (25 January to late 9 April 2020) was dominated by infections acquired overseas (59.5% of cases). 3 The second wave, which commenced in May 2020, was characterised by locally acquired infections (91% of cases); genomic sequencing indicated that the two transmission networks during this wave originated with infected people in hotel quarantine. 3 To reduce community transmission, the Victorian government introduced compulsory mask‐wearing, curfews, travel restrictions, closure of non‐essential businesses, and limits on the permitted number of household visitors.…”

Forecasting COVID-19 activity in Australia to support pandemic response: May to October 2020

“…Recall that the model used the active-case R eff to characterise local transmission at the time of forecast, with transmission reverting to the transmission potential (TP) over time (see Section 4.2 for details; example R eff trajectories are shown in Section B.4). However the second wave in Victoria was dominated by localised outbreaks in health and aged care settings, and other essential services, where public health and social measures to constrain transmission had less impact than in the general population [5]. Over a 5-month period, the R eff was systematically greater than the TP, as described and evaluated in Golding et al [7].…”

“…The proportion of infected persons that were identified as cases was likely to be both very high, and to remain relatively constant over the study period. These cases include asymptomatic individuals who were identified through large-scale and systematically exhaustive contact tracing programs [5]. In comparison, in recent influenza seasons the probability that a person with influenza-like illness (ILI) symptoms would seek healthcare and have a specimen collected for testing (as estimated from Flutracking [32, 33] survey participants) was around 3–8% [16].…”

“…Nonetheless, in May 2020 a breakdown in infection prevention and control measures in the state of Victoria’s hotel quarantine system resulted in community exposure that developed into a second wave [4, 5]. COVID-19 (ancestral strain) case incidence peaked at 450 locally-acquired infections per day in the last week of July 2020 [5, 6]. This was substantially higher than the peak of 131 daily cases in the import-driven first wave.…”