  We modelled emergence and spread of the Omicron variant of SARS-CoV-2 in
Australia between December 2021 and June 2022. This pandemic stage exhibited a
diverse epidemiological profile with emergence of co-circulating sub-lineages
of Omicron, further complicated by differences in social distancing behaviour
which varied over time. Our study delineated distinct phases of the
Omicron-associated pandemic stage, and retrospectively quantified the adoption
of social distancing measures, fluctuating over different time periods in
response to the observable incidence dynamics. We also modelled the
corresponding disease burden, in terms of hospitalisations, intensive care unit
occupancy, and mortality. Supported by good agreement between simulated and
actual health data, our study revealed that the nonlinear dynamics observed in
the daily incidence and disease burden were determined not only by introduction
of sub-lineages of Omicron, but also by the fluctuating adoption of social
distancing measures. Our high-resolution model can be used in design and
evaluation of public health interventions during future crises.
