Parameter estimates and data sources
Model parameters are detailed in table 1. We used available published literature to inform parameter estimates. We used the following publicly available metrics for model fitting: regional cumulative cases in SW (tested and confirmed cases in hospital), and deaths (daily/cumulative counts) from the Public Health England COVID-19 dashboard,14 and ONS weekly provisional data on COVID-19-related deaths.25 The case data are finalised prior to the previous 5 days, so we include all data until 14 May 2020, based on data reported until 18 May 2020. The mortality data from ONS do not explicitly state the number of COVID-19-related deaths occurring in hospital, but they do report this value nationally (83.9% of COVID-19 deaths in hospital, as of 17 April 2020). We assume that this percentage applies to the SW data and rescale the mortality to 83.9% to represent an estimate of total deaths in hospital.
Table 1  Parameter estimates used in the model and their sources. The distributions of unknown parameters are shown in online supplemental figure S1A for the best 100 fits
Symbol  Description  Uniform prior (min and max) or point estimate
1 / η  Duration of the non-infectious exposure period  5.1 days41
δ  Percentage of infections which become symptomatic  82.1%42; vary between 73.15% and 91.05%
1 / μ  Duration of symptoms while not hospitalised (independent of outcome)  Vary between 2 and 14 days
1 / ρ  Duration of stay in acute bed (independent of outcome)  Vary between 2 and 14 days
γ  g  Percentage of symptomatic cases which will require hospitalisation  0–4=0.00%, 5–17=0.0408%, 18–29=1.04%,30–39=2.04%–7.00%, 40–49=2.53%–8.68%,50–59=4.86%–16.7%, 60–69=7.01%–24.0%,70+=9.87%–37.6%16
1 / ψ  Duration of stay in IC bed (independent of outcome)  3–11 days43
ϵ  Percentage of those requiring hospitalisation who will require IC  Vary between 0% and 30%
ω  g  Percentage of those requiring IC who will die  0–4=0.00%, 5–17=0.00%, 18–29=18.1%,30–39=18.1%, 40–49=24.7%,50–59=39.3%, 60–69=53.9%,70+=65.3%43
κ  Percentage of those requiring acute beds (but not IC) who will die  Vary between 5% and 35%
school  Percentage of 0–18 year-olds attending school after 23 March 2020  Assume 5%
distancing  Percentage reduction in contact rates due to social distancing after 15 March 2020  Vary between 0% and 50%
lockdown  Percentage reduction in contact rates due to lockdown after 23 March 2020  Retail/recreation: Bristol 86%, Bath 90%, Plymouth 85%, Gloucs 84%, Somerset 82%, Devon 85%, Dorset 84%44Transit stations: Bristol 78%, Bath 71%, Plymouth 65%, Gloucs 69%, Somerset 67%, Devon 66%, Dorset 63%44Vary between 63% and 90%
R  0  Initial reproductive number of COVID-19  1.63–3.9524
endphase  Time taken to fully adjust (across the population, on average) to new interventions  Vary between 1 and 31 days
IC, intensive care.