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Publication - Research and analysis

Coronavirus (COVID-19): modelling the epidemic

Published
21 May 2020
Directorate
Constitution Directorate
Topic
Coronavirus (COVID-19) in Scotland
ISBN
9781839607554

Report presents the approach taken by the Scottish Government in modelling the COVID-19 epidemic in Scotland, both in terms of the spread of the disease through the population (epidemiological modelling) and of the demands it will place on the system, for example in terms of health care requirements

View supporting documents Supporting documents

What the modelling tells us

Figure 1 shows the movement of Rt since February. Before the "stay at home" restrictions were put in place Rt was above 1, and likely to have been between 4 and 6 before any interventions were put in place.

The model estimates the Rt value for Friday 8th May to be between 0.7 and 1.0.

Figure 1: R t for Scotland, 2020
Figure 1. A graph showing the trends in the Rt value over time, as calculated by the model. The graph show step changes downwards at the point when each intervention was introduced. This figure shows Rt to fall below 1.0 on the 23rd of March, when the “stay at home” advice was given.

Source: Scottish Government modelled estimates using Imperial College model code,
Source: Actual data from https://www.gov.scot/publications/coronavirus-covid-19-trends-in-daily-data/

Figure 2 shows the epidemiological model forecasts which suggest that, given the present set of interventions, this epidemic curve shows signs of reducing.

Figure 2: Short term modelled forecast number of deaths from Covid-19 in Scotland, May 2020
Figure 2. A barchart showing daily numbers of deaths caused by Covid-19 in Scotland between 21st February and 8th May, 2020. Overlain on this is the “estimated deaths” result from the model, which smooths out the cyclical weekly pattern in the reported numbers, due to fewer deaths being registered over a weekend. The model results suggest deaths in Scotland peaked around 19th March and have been steadily declining since then.

Source: Scottish Government modelled estimates using Imperial College model code,
Source: Actual data from https://www.gov.scot/publications/coronavirus-covid-19-trends-in-daily-data/

For the logistics model, short term forecasts for hospital bed occupancy predict a steady decline over the next two weeks, following the end of a plateau of around 1,500 people three to four weeks ago. The medium term forecast (figure 3) shows a similar story over the next few months, with a steady decline, but very little chance of reducing hospital occupancy due to Covid to zero. This assumes that we maintain the current "stay at home" arrangements, and there is no change in adherence to these. If guidance changes, this forecast will no longer apply.

Figure 3: Logistical model medium term forecast of number of people requiring a hospital bed from Covid-19 in Scotland, 2020
Figure 3. A graph showing the modelled forecast of the most likely number of people in Scotland requiring a hospital bed due to Covid-19, along with better and worse case scenarios. In this figure, the most likely number of people requiring hospital treatment declines from around 2000 in early April, to below 500 in July.

Source: Scottish Government modelled estimates using outputs from the Imperial College model code,
Source: Actual data from https://www.gov.scot/publications/coronavirus-covid-19-trends-in-daily-data/

There is still some uncertainty regarding the actual number of people in hospital with Covid-19, with the chart above comparing a lower bound for this number (based on the number of people in hospital that have tested positive for Covid-19) and an upper bound (additionally including suspected cases that have not tested positive).

The medium term modelling also provides us with the following forecast of the number of ICU beds required (figure 4). In recent weeks, it has looked as if the actual count of people in ICU has been falling faster than the model suggests, although the most recent data seems to show the potential for a second plateau, or even another rise.

Figure 4: Logistical model medium term forecast of number of people requiring an intensive care from Covid-19 in Scotland, 2020
Figure 4. A graph showing the modelled forecast of the most likely number of people in Scotland requiring intensive care due to Covid-19, along with better and worse case scenarios. In this figure, the most likely number of people requiring intensive care treatment declines from around 200 in early April, to below 50 in July.

Source: Scottish Government modelled estimates using outputs from the Imperial College model code,

Source: Actual data from https://www.gov.scot/publications/coronavirus-covid-19-trends-in-daily-data/

Contact

Email: modellingcoronavirus@gov.scot

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