What Vaccination Rate(s) Minimise Total Societal Costs after 'Opening Up' to COVID-19? Age-Structured SIRM Results for the Delta Variant in Australia (New South Wales, Victoria and Western Australia)

Abstract

Using an age-structured, stochastic SIRM model, calibrated to Australian data post July 2021 with community transmission of the Delta variant, we project possible public health outcomes (daily cases, hospitalisations, ICU beds, ventilators and fatalities) and economy costs for three states: New South Wales (NSW), Victoria (VIC) and Western Australia (WA). NSW and VIC have had on-going community transmission since July 2021 and have been in ‘lockdown’ to suppress transmission. WA did not have on-going community transmission nor was it in lockdown at the model start date (11 October 2021) but did maintain strict state border controls. We project the public health outcomes and the economic costs of ‘opening up’ (relaxation of lockdowns in NSW and VIC or fully opening the state border for WA) at alternative vaccination rates (70%, 80% and 90%), compare peak patient demand for ICU beds and ventilators to staffed state-level bed capacity, and calculate a ‘preferred’ vaccination rate that minimises societal costs that varies by state. We find that the preferred vaccination rate for all states exceeds 80% and that the preferred population vaccination rate is increasing with: (1) the speed of vaccination; (2) the effectiveness (infection, hospitalisation and fatality) of the vaccine; (3) the lower is the daily lockdown cost; (4) the larger are the public health costs from COVID-19; (5) the higher is the rate of community transmission before opening up; and (6) the less effective are the public health measures after opening up.