Britain’s contact-tracing app is expected to be needed until spring 2022, according to the terms of a contract drawn up between the Health Secretary and its developers.

The NHS Covid-19 App, which uses Bluetooth to detect “close contacts” between two smartphones, was launched in September last year as a way of speeding up manual contact-tracing of coronavirus cases.

The contract is the clearest signal that the use of digital contact-tracing is set to continue long after the vast majority of the UK population has been vaccinated twice.

According to a contract between the Department of Health and Zühlke Engineering, the Swiss company that develops and maintains the app, Zühlke will keep the app running until at least September this year for a fee of £10.2 million.

But the contract gives Matt Hancock, the Health Secretary, the right to extend work on the app at short notice for up to six further months, until March 2022.

The contract also stipulates that Zühlke must support the scaling of the app to up to 50 million downloads, more than double the number of users it currently has.

The app has been downloaded more than 24.5 million times, according to the Department of Health.

NHS contact tracing app – What is the technology behind it?

According to a peer-reviewed study in the journal Nature, whose authors included Oxford’s Christophe Fraser, who helped develop the app, the UK’s NHS Covid-19 app has helped prevent thousands of deaths.

The study found an estimated 1.7 million “exposure notifications” were sent to users, a warning that they have come into close contact with someone who later reported coronavirus symptoms.

The app measures a close exposure between people using Bluetooth signals from their phones. It can then warn them remotely and anonymously if they have been in contact with someone, even if they are a stranger.

The paper estimated 284,000 to 594,000 people avoided catching coronavirus as a result, based on two different analyses. This translated to 4,200 or 8,700 deaths being avoided.

The NHS Covid-19 app deletes most data stored on users’ smartphones after 28 days. However, some anonymous, analytical data is kept by the Government to study the pandemic, which can be held for up to 20 years. Users can choose to uninstall and delete the app from their phones at any time.

NHS contact tracing app – What is it and how does it work?

Last May, MPs called for a Bill to force the Government to delete all data gathered by the app after the pandemic was over. Computer experts warned at the time contact-tracing apps could signal a “mission creep into surveillance”.

Britain’s contact-tracing app runs on a system built by Apple and Google, which ensures its information sharing is decentralised, ensuring greater privacy.

The tech giants have, as part of the rules for using their software, said they will disable the contact-tracing app tools once the pandemic has come to an end.

A Department of Health spokesperson said: “The app has been designed with user privacy in mind, so it tracks the virus not people, and uses the latest in data security technology to protect privacy.

“It is a key tool in our pandemic response and will remain so for the foreseeable future.”