Coronavirus (COVID-19): modelling the epidemic (Issue No. 31)

Technical Annex - New Year medium term modelling approach

The modelling is done using an SEIR model based on confirmed cases, from 1 July to the end of March 2021. There is a degree of certainty up until the start of the festive bubble and beyond this point, uncertainty increases (see Figure 9).

Historical modelling, based on a single population of potentially infectious people, has been updated to provide a richer picture of the likely impacts of the festive period, by splitting the population into three age bands: 0-17, 18-64, 65+. These breakdowns allow us to examine the interplay between contacts across different ages, thereby assessing how the infection is likely to spread across the population.

Contact between people has been modelled using data from the Scottish Contact Survey (SCS). This is a behavioural survey, asking questions to panels of people who have been recruited to be broadly representative of the Scottish population. SCS does not include participants under the age of 18, which therefore means contacts for this age group (0-17) have been taken from the CoMix behavioural study, which is a sample representative of the UK.

The modelling simulates changes in contact patterns over the Festive period and afterwards. However, it does not simulate the likely mixing that will take place over these timescales, resulting from households travelling and then returning to their normal environments. This will circulate the infection more and needs to be accounted for. The most similar effect we can find in the history of Covid-19 is from the beginning of Summer, when land and air travel to Scotland was re-opened. We use the increases in infections seen at that time to assess potential changes to the R value in the New Year, which are then applied to the whole population (not accounting for differences in age).

Tables 2 and 3 provide the underlying data used in the section above on "What the modelling tells us about Hospital bed and ICU bed demand". They are based on modelling undertaken by Scottish Government (for more information see research findings issue 1).

The purpose of these predictions is to support a decision on what measures are needed in different parts of Scotland. As part of the medium term modelling, these predictions are not intended as short term forecasts (less than two weeks, for which management information is more appropriate), but the initial weeks are provided for completeness.

As the middle, lower and upper ends of the range are presented for each health board, the aggregate cannot be used as a prediction of the number of beds required in Scotland as a whole.

* indicates that the middle of the range is less than 5. Values in this table give an interval, actual occupancy could be higher or lower.

* indicates that the middle of the range is less than 5. Values in this table give an interval, actual occupancy could be higher or lower.