How will mass-vaccination change COVID-19 lockdown requirements in Australia?

Abstract

BackgroundTo prevent future outbreaks of COVID-19, Australia is pursuing a mass-vaccination approach in which a targeted group of the population comprising healthcare workers, aged-care residents and other individuals at increased risk of exposure will receive a highly effective priority vaccine. The rest of the population will instead have access to a less effective vaccine. MethodsWe apply a large-scale agent-based model of COVID-19 in Australia to investigate the possible implications of this hybrid approach to mass-vaccination. The model is calibrated to recent epidemiological and demographic data available in Australia, and accounts for several components of vaccine efficacy. FindingsWithin a feasible range of vaccine efficacy values, our model supports the assertion that complete herd immunity due to vaccination is not likely in the Australian context. For realistic scenarios in which herd immunity is not achieved, we simulate the effects of mass-vaccination on epidemic growth rate, and investigate the requirements of lockdown measures applied to curb subsequent outbreaks. In our simulations, Australia's vaccination strategy can feasibly reduce required lockdown intensity and initial epidemic growth rate by 43% and 52%, respectively. The severity of epidemics, as measured by the peak number of daily new cases, decreases by up to two orders of magnitude under plausible mass-vaccination and lockdown strategies. InterpretationThe study presents a strong argument for a large-scale vaccination campaign in Australia, which would substantially reduce both the intensity of future outbreaks and the stringency of non-pharmaceutical interventions required for their suppression.

Simulating Transmission Scenarios of the Delta Variant of SARS-CoV-2 in Australia

“…Construction works were temporarily paused across Greater Sydney during 19-30 July 2021 (inclusive), with the temporary "construction ban" lifted on 28 July (28,29). Within the considered timeline, the actual incidence growth rate has reduced from β I = 0.098 (17 June -13 July), to β II = 0.076 (17 June -25 July), to β III = 0.037 (16)(17)(18)(19)(20)(21)(22)(23)(24)(25), as detailed in Supplementary Material: Growth rates.…”

“…This relatively high SD compliance was required in addition to other restrictions (TR, CI, HQ), set at moderate levels of both macro-distancing (CI = 0.7 and HQ = 0.5), and interaction strengths: CI w = HQ w = CI c = HQ c = 0.25, CI h = 1.0, and HQ h = 2.0 (1). The follow-up work (17) quantified possible effects of a mass-vaccination campaign in Australia, by varying the extents of pre-pandemic vaccination coverage with different vaccine efficacy combinations. This analysis considered hybrid vaccination scenarios using two vaccines adopted in Australia: BNT162b2 (Pfizer/BioNTech) and ChAdOx1 nCoV-19 (Oxford/AstraZeneca).…”

“…We utilised an agent-based model (ABM) for transmission and control of COVID-19 in Australia that has been developed in our previous work ( 1 , 17 ) and implemented within a large-scale software simulator (AMTraC-19). The model was cross-validated with genomic surveillance data ( 6 ), and contributed to policy recommendations on social distancing that were broadly adopted by the World Health Organisation ( 18 ).…”

“…Different contact rates specified within diverse social contexts (e.g., households, neighbourhoods, communities, and work/study environments) explicitly represent heterogeneous demographic and epidemic conditions (see Supplementary Material : Agent-based model). The model has previously been calibrated to produce characteristics of the COVID-19 pandemic corresponding to the ancestral lineage of SARS-CoV-2 ( 1 , 17 ), using actual case data from the first and second waves in Australia, and re-calibrated for B.1.617.2 (Delta) variant using incidence data of the Sydney outbreak (see Supplementary Material : Model calibration).…”

Implications of COVID-19 Mitigation Policies for National Well-Being: A Systems Perspective

“…Hence, they should be considered measures of the last resort, to be avoided if at all possible. With the widening availability of vaccinations, they increasingly can be avoided [86], and indeed should be deferred. A second insight is the importance of maintaining employment to the extent possible, as employment is seen to be a major stratifying variable in the equity analysis.…”