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U.K. Study Shows Power of Digital Contact Tracing for COVID-19

Posted on by Dr. Francis Collins

COVID-19 cases in the United Kindom. Hands hold a smart phone with the NHS COVID-19 app
Credit: Adapted from Getty Image and Wymant C, Nature (2021)

There’s been much interest in using digital technology to help contain the spread of COVID-19 in our communities. The idea is to make available opt-in smart phone apps that create a log of other apps operating on the phones of nearby participants. If a participant tests positive for COVID-19 and enters the result, the app will then send automatic alerts to those phones—and participants—who recently came into close proximity with them.

In theory, digital tracing would be much faster and more efficient than the challenging detective work involved in traditional contract tracing. But many have wondered how well such an opt-in system would work in practice. A recent paper, published in the journal Nature, shows that a COVID-19 digital tracing app worked quite well in the United Kingdom [1].

The research comes from Christophe Fraser, Oxford University, and his colleagues in the U.K. The team studied the NHS COVID-19 app, the National Health Service’s digital tracing smart phone app for England and Wales. Launched in September 2020, the app has been downloaded onto 21 million devices and used regularly by about half of eligible smart phone users, ages 16 and older. That’s 16.5 million of 33.7 million people, or more than a quarter of the total population of England and Wales.

From the end of September through December 2020, the app sent about 1.7 million exposure notifications. That’s 4.4 on average for every person with COVID-19 who opted-in to the digital tracing app.

The researchers estimate that around 6 percent of app users who received notifications of close contact with a positive case went on to test positive themselves. That’s similar to what’s been observed in traditional contact tracing.

Next, they used two different approaches to construct mathematical and statistical models to determine how likely it was that a notified contact, if infected, would quarantine in a timely manner. Though the two approaches arrived at somewhat different answers, their combined outputs suggest that the app may have stopped anywhere from 200,000 to 900,000 infections in just three months. This means that roughly one case was averted for each COVID-19 case that consented to having their contacts notified through the app.

Of course, these apps are only as good as the total number of people who download and use them faithfully. They estimate that for every 1 percent increase in app users, the number of COVID-19 cases could be reduced by another 1 or 2 percent. While those numbers might sound small, they can be quite significant when one considers the devastating impact that COVID-19 continues to have on the lives and livelihoods of people all around the world.


[1] The epidemiological impact of the NHS COVID-19 App. Wymant C, Ferretti L, Tsallis D, Charalambides M, Abeler-Dörner L, Bonsall D, Hinch R, Kendall M, Milsom L, Ayres M, Holmes C, Briers M, Fraser C. Nature. 2021 May 12.


COVID-19 Research (NIH)


Christophe Fraser (Oxford University, UK)


  • Eileen Natuzzi says:

    While apps may speed up contact notifications they do not offer one to one education or the ability to do severity of illness assessment. Having worked on COVID 19 case investigations there is great deal of value to speaking with someone who is infected or exposed. During a phone conversation the risks a person has for developing severe disease or household member with significant risks can be discussed. Education is important. So while apps may be efficient at notifying people of potential exposure reaching out to them must continue.

  • anyonefort says:

    If this positive account is accepted, think how much better had the app been available at the same time as Ireland (early July 2020), or Latvia (late May 2020). And if it fully worked across borders – even Scotland and Northern Ireland represent discontinuities. (For anyone outside the United Kingdom, there are four nations. This app only worked in two, England and Wales.)

    The QR codes have been something of a joke. Many places which you might have expected to have them not actually been displaying them – for example shops. Their size made them difficult to scan reliably, and some venues only asked for surname and phone number not expecting you scan at all.

  • Steve White says:

    I appreciate the efforts people public health workers made to fight the epidemic, but I am skeptical it was very effective. Unlike VDs, one SARS2 infected person can infect dozens of other people without touching them. I understand the app retroactively addresses this problem – after you find out you are infected, the people you got physically close to are notified – but they find out after the fact – and after they have likely infected more people. It appears very hard to catch up.
    Unlike TB, where an infected person stays infected for a very long time, and can keep spreading it, Covid infection rapidly resolves, in most cases – or the person is identified and isolated, because they are very sick. So, when you find the infected person, you are not finding someone who will go on for months or years infecting new people, as you are with TB.

    SO, I understand, an app, if widely adopted, could reduce both these problems, – I also understand no one was “forced” to use the app – but I believe there are very strong arguments against the surveillance society and though semi-voluntary at first, these are growing and becoming inescapable. Because the technology exists for it, pretty much everyone who goes for a drive in my urban area has their license plate automatically recorded by video cameras. They are everywhere. Soon, cell phone apps will make any kind of travel, on foot or bicycle, equally impossible to keep confidential. Is this a good thing?

  • Jo Ann Scott says:

    There are reports that a person who is 2 weeks past the second dose of vaccine is unlikely to get, or spread, the virus. If this is true, is there any reason for a fully vaccinated person to install the app?

  • Mayling says:

    Yet perhaps another example of how covid stratifies society along socio-economic boundaries. Those programmers writing the apps are unlikely to live in multi generational homes with crowded living conditions with questionable ventilation systems. Is a smart phone app using GPS coordinates able to tell if there is a wall, floor or ceiling between you and your neighbor who may be covid infected?
    Singapore has reports of how well this type of method worked. Someone should also see how well it worked in Hong Kong. Better yet, what did China do in Wuhan?
    If free societies want to become surveillance states and the public is not informed, who’s onus is that on?
    Complex situations require humility, not a “all you gotta do is” attitude. Perhaps this is one example of failure in “group think” in places of higher education. Just look at what type of research gets R01 funding. Having the ability to see when one is jumping on a bandwagon without sufficient information is also meaningful to acknowledge.

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