NHS Test and Trace had critical impact on reducing COVID-19 transmission, new model finds

NHS Test and Trace had a significant impact on driving down levels of COVID-19 transmission between June 2020 to April 2021, new modeling published today shows.

From June 2020 to April 2021, testing, contact tracing and self-isolation directly prevented somewhere between 1.2 million and 2 million COVID-19 infections.

Since its inception, NHS Test and Trace has played an important role in countering this virus - along with the phenomenal vaccination programme - contacting over 14.9 million people from across the country and breaking chains of transmission to stop outbreaks.

From a standing start NHS Test and Trace has built a huge testing capacity, with over 262 million tests now completed. This includes the free PCR test offer for people with symptoms and people who are double jabbed and are identified as close contacts, in addition to regular rapid testing for people without symptoms.

With around one in three people with COVID-19 showing no symptoms, regular testing and contact tracing, alongside the wall of defence built by the vaccination programme, are fundamental to ongoing efforts to keep people safe and help the return to a more normal way of life.

The Canna model

The 'Canna' model published today estimates the impact of test, trace and self-isolation, coordinated by NHS Test and Trace, on COVID-19 transmission from June 2020 to April 2021.

The modeling compares NHS Test and Trace statistics with ONS infection survey data, and estimates the timing and compliance rates of isolation to determine the overall level of transmission reduction from testing, contract tracing and self-isolation. This work is being used to develop new value-for-money analysis that will help guide future decision making.

Key findings

The Canna model found that NHS Test and Trace had a critical impact on identifying cases of COVID-19 and reducing onward transmission. Its key findings were:

  • From June 2020 to April 2021, testing, contact tracing and self-isolation directly prevented between 1.2 million and 2 million COVID-19 infections. This does not take into account the impact of onward chains of transmission which could be significantly higher.
  • Since 10 August 2020, NHS Test and Trace identified between 25% and 65% of the total infectious population as either a case or a contact.
  • Since 10 August 2020, the transmission reduction from test, trace and self-isolation varied over time from 10-28%.
  • There are several periods (August 2020, November 2020, January - April 2021) where test, trace and self-isolation potentially brought the R rate down below 1, which would have been crucial in reducing the duration and impact of lockdowns.
  • The model also considers the impact over and above a counterfactual where people with symptoms still isolate without any access to testing.

For more information on the Canna model and how it works, please click here.

The Canna model considers the historical impact of test and trace on transmission given reasonable assumptions. Establishing the full social and economic value of test and trace requires an economic assessment of this impact.

We are currently undertaking an economic assessment to understand and, where possible, quantify the direct and wider social and economic benefits to preventing COVID-19 infections.


  • A panel of external experts from academia provided advice on the modeling throughout its development. Given the constraints, the panel regarded the core assumptions and structure as appropriate for determining the impact on transmission of test, trace and self-isolation.


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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