The Scottish Government modelled the estimated impact of the Test and Protect (T&P) strategy using the Canna model developed by the UK Government Department of Health and Social Care (DHSC). The model estimates the reduction in transmission of Covid-19 due to Test and Protect by determining the proportion of all infectious individuals undergoing isolation over the time course of their infectious period.
The Canna model compares the observed values of R, obtained with both symptomatic and asymptomatic testing and self-isolation of both household and non-household contacts, with values of R obtained from two modelled scenarios:
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Full impact model: No T&P and no self-isolation for individuals with Covid-like symptoms or their contacts, but other restrictions, e.g. social distancing, lockdowns etc., remain in place.
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Counterfactual model: A counterfactual scenario with no T&P, but all individuals with Covid-like symptoms self-isolate, without ever taking a test, along with their household contacts.
The difference between the observed and modelled values of R is calculated for both models, and the marginal impact directly attributable to T&P is assumed to lie within these two values. Symptomatic case detection and household contact isolation are considered in both the full impact model and the counterfactual and are major contributors to transmission reduction. Any additional marginal impacts from Test and Protect come exclusively from non-household contact tracing and asymptomatic testing.
The results from the Canna model have been considered internally by Scottish Government and have not yet been published.
This model is one of a series used by the Scottish Government during the pandemic to model the spread and levels of Covid-19 in Scotland. Many of the results of these models have been published in the Modelling the Epidemic series of reports.
If you have any questions regarding the contents of this repository, please contact sgcentralanalysisdivision@gov.scot.
This repository is available under the Open Government Licence v3.0.