Australian researchers have modelled the various combinations of public health and social measures best suited to tackle new waves of COVID.
The study, published 20 January 2023 in The Lancet Regional Health – Western Pacific, found that no matter what policy was implemented, high numbers of infections and deaths were likely, with 4.2 million infections and 8,100 deaths on average, and there was a clear trade-off between the economic costs and health benefits of escalating public health measures, such as wearing masks and working from home.
They also found that any schedule of vaccine boosters was more beneficial than not providing ongoing vaccination, and overall, the highest-ranking policy combination was more stringent public health measures, with two further vaccine doses for the over 30s and promotion of increased mask-wearing – without government provision of respirators.
Lead author, Dr Joshua Szanyi from the Population Interventions Unit at the University of Melbourne’s Centre for Epidemiology and Biostatistics, explained that COVID related policy decisions must be made in the context of substantial uncertainty, posing a significant challenge for policy makers.
“In this complex environment it is increasingly important that the benefits and drawbacks of interventions are rigorously and systematically compared – including from a cost effectiveness perspective,” Dr Szanyi said.
“In response to these needs we developed an integrated epidemiologic and economic simulation model to determine the optimal of 104 illustrative policy packages for the state of Victoria.
“We used an agent-based model with a daily cycle length and 5,000 agents scaled up to represent the Victorian population to estimate morbidity, mortality, and costs over 12 months from October 2022 for each scenario.”
The model was initially calibrated to the first COVID waves in Australia and New Zealand and has previously been used to inform policy in Victoria.
Each policy was modelled in the context of nine future variant scenarios – eight combinations of low or high virulence, low or high antigenic similarity to Omicron, and low or high immune escape capacity (as well as one scenario with no new variant) – emerging in November 2022, following successive periods of Omicron BA.1/2 and Omicron BA.4/5 dominance from April 2022.
All 936 scenarios (the 104 policy packages combined with the nine viral variants) were run 500 times each, using fresh input parameters, and the policies were then ranked based on cumulative deaths, hospital system pressure, and cost effectiveness from both health system and health system plus GDP perspectives.
“More compared to less stringent PHSMs reduced cumulative infections, hospitalisations, and deaths by an average of 25%, 24% and 24% respectively across 468 policy comparisons, but also increased time in stage ≥3 (out of 5) PHSMs by an average of 42 days – 23 days for low virulence and 70 days for high virulence variants,” the authors said.
“Any further vaccination from October 2022 decreased hospitalisations and deaths by 12% and 27% respectively compared to no further vaccination, however the cumulative number of infections increased by 10% due to vaccination preferentially decreasing hospitalisation rates that were used to dynamically set PHSM stages.”
Any further vaccination was of marginal cost-effectiveness from a health system perspective, costing an average of AUD $77,500 per health-adjusted life year gained for vaccinating ≥60-year-olds, and AUD $41,600 for 30- to 59-year-olds.
However, vaccination also resulted in 36% fewer days in Stage ≥3 PHSMs, usually making it a cost-saving intervention from a health expenditure plus GDP perspective, and high versus low vaccine coverage reduced deaths by 15% and reduced time in Stage ≥3 PHSMs by 20%.
Promotion to increase mask wearing or government provision of respirators during large outbreaks reduced cumulative infections, hospitalisations, and deaths over the 12 months by 1% to 2%, and reduced the number of days where hospital occupancy rates exceeded 750 COVID patients by 2%, up to 4% or 5% in the context of highly virulent variants.
“To our knowledge, our study is the first that utilises a dynamic disease transmission model combined with an integrated economic evaluation framework, to systematically compare COVID policy intervention packages while accounting for ongoing SARS-CoV-2 evolution and waning population immunity… providing a framework for assessing optimal pandemic policy in the face of a rapidly evolving and uncertain future,” the authors concluded.
“At a high-level, we found that a considerable degree of COVID disease burden should be expected in the future, with modelled interventions only able to partly mitigate pandemic-associated morbidity and mortality in the medium-term.”