Researchers from the University of Oxford and the Alan Turing Institute have found that the NHS COVID-19 contact tracing app may have prevented 200,000-900,000 people becoming infected between October 1st 2020 and December 31st.

The app, which was downloaded onto 21 million smartphones out of 33.7 million compatible units, was used to alert users about the COVID-19 alert level in their area and whether they had come into contact with anyone who had tested positive for the virus. For every person who shared their positive test result with the app, an average of 4.4 people were alerted and told to self-isolate. Most alerts occurred during the second half of December when transmission rates increased, driven by the highly transmissible B117 variant.

Through analysing over 1.5 million notifications sent by the app, the researchers found that between 200,000-900,000 infections were averted. For every 1% of people who used the app, the number of cases fell by 0.8%-2.3%.

Christophe Fraser, Professor of Pathogen Dynamics at Oxford University’s Big Data Institute, said “Our work confirms the NHS COVID-19 app is sending exposure notifications to relevant contacts. Isolating when receiving a notification from the app contributes to preventing the spread of the virus.”

When the researchers compared two areas with similar demographics and levels of COVID restrictions, the area with the higher uptake of the app had significantly fewer COVID cases.

“The data also suggests that if all areas had reached a usage similar to the areas with the highest uptake, we would have had 200,000 to 400,000 fewer cases on top of those averted already” added David Bonsall, Principal Investigator at the Wellcome Centre for Human Genetics at Oxford University’s Nuffield Department of Medicine.

Research produced by the Alan Turing Institute led to the app being updated to better identify high-risk contacts, and increase the number of notifications sent out per confirmed test. Before the update, a 1% increase in the number of people using the app reduced cases by 0.3-1.1%. The update reduced cases further to 0.9-2.3%.

Dr Luca Feretti, a researcher at Oxford University’s Big Data Institute, stressed the need for international cooperation to improve the functioning of contact tracing apps, commenting “Our research shows that improving the app significantly increases the number of infections it can prevent. It is essential that countries share these improvements between national apps. The contact tracing apps need to remain tuneable so they adjust to using the best available technology to combat the evolving epidemic.”

Image: John Cameron via

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