The NHSX's contact-tracing app might have actually worked

A new study shows that the number of cases on the Isle of Wight dropped significantly after both manual and digital contact-tracing programs launched. Should we give the app more credit?
Written by Daphne Leprince-Ringuet, Contributor

Analysis by the scientists who worked on the first version of NHSX's contact-tracing app might help provide a tentative answer to the question that is dividing politicians and experts: does the technology actually work?

A team of researchers from Oxford University's Nuffield Department of Medicine has drawn up preliminary insights into the impact of contact tracing on the Isle of Wight, which started in early May, hand-in-hand with the much-hyped trial of NHSX's contact-tracing app.

The results cannot be attributed to the app on its own but are nevertheless encouraging. Before the manual Test and Trace program launched as a pilot on 5 May, alongside the app release, the R rate on the Isle of Wight was not far from being the highest in the country. It became the tenth lowest after the program started and the app was made available. The R rate is the average number of infections triggered by each individual who gets ill.

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The NHSX contact-tracing app that was trialed on the Isle of Wight let users self-report cough or fever, and anonymously notified other users who had been in recent contact with the symptomatic individual, offering generic guidance on how to reduce the risk of transmission, but without instructing to self-isolate or quarantine.

More than 54,000 residents downloaded the technology, which represents about 38% of the population. During the month of May, 1,524 users reported symptoms in the app, resulting in 1,188 receiving an exposure notification. The manual contact-tracing program, in contrast, sent requests to self-isolate to only 163 individuals on the basis of reports from a total of 160 cases.

"These two approaches are complementary," reads the research paper. "(Manual contact tracing) is a more familiar intervention and a phone call may be more effective once received, but the speed of notification of (the app) may be critical given the speed of COVID-19 transmission."

App or no app, it seems logical that the start of a Test and Trace program of any sorts would coincide with a drop in case counts. But the researchers found that the change was noticeable in the Isle of Wight, more so than in the rest of England, even after the launch of a similar intervention. A manual Test and Trace program effectively started nationally at the end of May, albeit without a contact-tracing app.

Based on hospital case counts and publicly available data about COVID-19 positive swabs among the wider community, the team estimated the maximum likelihood of R rates in the rest of England after Test and Trace interventions. 

"The reproduction number R on the Isle of Wight was consistently lower than the 'national' rate," says the report. On the island, the R rate dropped from 1.3 before the start of the program, to 0.5 recently, which compares to an estimate of 0.875 in the rest of the nation after the launch of Test and Trace – suggesting that some factors might have come into play on the island to further strengthen local control of the virus. 

Despite the numbers, the researchers stressed that the analysis could not establish a link between Test and Trace and the drop in the R rate on the Isle of Wight, let alone claim with certainty that the app is the reason that the program worked better compared to the rest of the country.

After all, the contact-tracing program started in the rest of England at the same time that lockdown measures relaxed, which could explain why the R rate hasn't decreased as significantly in the rest of the country.

It could also be that residents on the Isle of Wight were more receptive to the huge advertising campaign that came with the early launch of Test and Trace, and followed guidance more closely. Or, that the contact-tracing program did a better job of staying ahead of the virus; or that people self-isolated more carefully when they received positive test results. Or, it could be that the contact-tracing app actually made a difference.

SEE: Contact-tracing app: How did the UK go so badly wrong?

Michelle Kendall, senior researcher at Oxford University's Nuffield Department of Medicine, and lead author of the report, told ZDNet: "We can clearly see looking at the number of cases and the R value on the Isle of Wight that something very positive occurred. By the end of June the island reported less than one case a week.

"To tease apart the impact of the app we would need to know things like: of the people testing positive, how many were already self-isolating because they had received an app notification? That would tell us how well the app was performing in staying one step ahead of the virus and giving infected people the information they needed so that they did not infect others," she added.

The suggestion that the app was an effective tool is likely to be met with a dose of skepticism. The NHSX contact-tracing app ran into a series of setbacks after it entered its test phase on the Isle of Wight. The technology was eventually axed by health authorities, after it was revealed that the app struggled to recognize the vast majority of iOS devices.

Many other countries have launched their own versions of the technology to support manual contact tracing, but even the engineers behind some of the apps have warned of the limitations of the tool. Jason Bay, one of the creators of Singapore's TraceTogether app, has publicly declared that "automated contact tracing is not a coronavirus panacea".

SEE: Contact tracing: The app is 'urgent and important', but there's still no launch date in sight

The shortcomings of Bluetooth technology, which constitutes the backbone of the majority of contact-tracing apps, is the cause of most experts' distrust. A recent study from Trinity College Dublin found that Bluetooth signals are inaccurate when it comes to estimating proximity, which means that contact-tracing apps can't be trusted in some environments.

Researchers from the Oxford University's Nuffield Department of Medicine remain confident that a contact-tracing app could play a role in controlling the epidemic. 

"The app has the potential to fulfill several important tracing functions," David Bonsall, one of the authors of the latest analysis of the Isle of Wight trials, told ZDNet. "We estimate that a 48-hour delay to contact tracing could result in twice as many new infections compared to a digital system that sends instant alerts at the point people develop symptoms."

For now though, no certain conclusions can be drawn without further data. Bonsall and his team's study has been published as a preprint, and still needs to be peer-reviewed.

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