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NHS Track and Trace – not fit for purpose?

On Thursday September 25, the much-vaunted NHS Track and Trace App was launched in England. The ability to make a link between those who have the virus with others who have been in the company of infected people for extended periods is undoubtedly a positive step along the road to managing the pandemic, but there are question marks over the App’s fitness for purpose.

Intrinsically the Track and Trace App works using a technology known as Bluetooth, which enables short-range communications between mobile devices. Using Bluetooth, it is possible to determine which devices have been in close(ish) proximity to each other, the theory being that it is therefore possible to detect when a person infected with COVID-19 has been near to others who might subsequently be infected as a result of the interaction.

The detail is a little more complex, and determination of which interactions are of concern ultimately involves the length of the close interaction (in minutes) and the distance between the devices – the closer the two devices are, and the longer the Bluetooth interaction between the devices, the more the situation is regarded as “threatening”.

Bluetooth has a very limited range, but “devices typically have a range of about 30 feet [some sources say up to 30m], do not require line of site to send a signal, and can even go through walls.” So, in principle the idea sounds fine but let’s move on and consider a few scenarios that might be of concern.

Scenario 1

Person A lives in a flat or a terraced house. They leave their phone, loaded with the NHS Track and Trace App on overnight, often on the bedside table that is adjacent to a dividing wall. The phone happily exchanges Bluetooth messages with the neighbour’ s phone, which likewise has been left on and not too far from a dividing wall. Throughout the hours of darkness, the phones have been pinging each other for eight hours.

Unfortunately, the neighbour of Person A later tests positive for COVID-19. Person A only occasionally sees their neighbour, talks to them much less frequently and has never been in their house. However, because their phones have been interacting, Person A is now classed as having had lengthy close interactions with an infected person

Scenario 2

A family go to the seaside for the day, and when they arrive in their car the overnight rain hasn’t cleared away. Awaiting the forecast weather improvement, they sit in the car in the beachfront car park, watching the breakers. A phone in the car, loaded with the NHS Track and Trace App, is on and merrily sending out Bluetooth signals.

The family are not alone though, and in the adjacent parking space much the same is happening. But there is also a phone loaded with the NHS Track and Trace App in this second car, and the two devices interchange data throughout the wait.

Again unfortunately, a person in the second car subsequently tests positive for COVID-19. Even though neither family get out of the car while the rain continues, indeed they don’t even open their vehicle’s windows, as far as the App is concerned the two groups have had close interaction over an extended period.

Scenario 3

Person A checks into a hotel and before getting to their room the only other people they see and interact with are behind the reception desk. Like in Scenario 1, when they get to their room, they leave their phone loaded with the NHS Track and Trace App on overnight, on the bedside table. Adjacent hotel rooms are often arranged bedhead to bedhead and the walls are thin, so the first guest’s phone which is sending out Bluetooth messages will be well within the range of the device of the other guest in the next room along the corridor. Again, during the night, the two phones have been pinging each other.

Unfortunately, the guest in the second room tests positive for the virus a few days after checking out. The person in the first room has never even seen the infected person let alone spoken to them, but the two phones have been near enough for a while meaning that Person A is now classed as having had close interactions with an infected person.

You will be getting the message by now. There are plenty of scenarios where two mobile devices running the NHS Track and Trace App might be in close proximity for a considerable time, without any risk whatsoever of the virus being transmitted – in scenarios 1 and 3 there are solid walls between the two, while in scenario 2 there is a car body and windows separating the two parties.

And yet, in all three cases, the uninfected parties will receive an alert from NHS Track and Trace, instructing them to self-isolate. This instruction is invidious in its own right, because all it says is that the owner of the device might have been infected with the virus, and must isolate for a period of up to 14 days. There’s no mention of where the interaction that could have resulted in transmission took place, and no mention of the date and the time or the period of the interaction. Apparently passing on these details is not allowed due to UK patient confidentiality laws. Note there is no mention the name(s) of the parties involved – just the date, time, period and place – but sharing even this is not permitted because it could supposedly enable the people involved to identify each other.

False positives

There are plenty of expert opinions that point to Bluetooth not being a reliable enough to rely on for contact tracing during an epidemic. A Singaporean government official wrote on Medium, “If you ask me whether any Bluetooth contact tracing system deployed or under development, anywhere in the world, is ready to replace manual contact tracing, I will say without qualification that the answer is, no.”

In a report in the New Scientist, Jess Morley of the University of Oxford said she would not be installing the app in its current form, because of privacy concerns and fear it would not work well. “If I thought it was genuinely going to work then I would potentially mind less about the other issues [such as privacy] but I think it’s problematically designed and probably likely to be quite ineffective. It’s that combination that makes me say no.”

Dr. Farzad Mostashari, the former national coordinator for health information technology at the Department of Health and Human Services in Australia told The Verge: “You could be through the wall from me in an apartment, and it could ping that we’re having a proximity event. You could be a on a different floor of the building and it could ping…”

Meanwhile an Irish study, where a similar App to the UK version is being used, found Bluetooth to be unreliable in determining a two metres distance, the critical measure when deciding whether a contact between people is close or not.

And more tellingly yet, a study by Richard J. Self, Senior Lecturer in Governance of Advanced and Emerging Technologies and MSc Mobile App Development student Jack Hider at the University of Derby reported: “It can confidently be stated that it will not be possible to use a smartphone app as the basis of a Track and Trace and risk assessment process for COVID-19 because no one will be confident that the warnings are accurate enough to avoid unnecessary and possibly very regular self-isolation...”

And yet here in the UK, people will be instructed to lockdown based on Bluetooth “evidence”, with no recourse to appeal if they believe the data is incorrect or there are extenuating circumstances that point to isolation being unnecessary.

Unexplained, unjustified

Being told by computer software to isolate for 14 days without it providing any details - why, where the supposed close interaction took place, the date and time, and how long the interaction was for - is the equivalent of being convicted of a crime without being able to see, review, question or challenge the evidence.

Computer systems can be buggy, especially in the early days. It is also obvious that there are situations where the App could provide an instruction to someone to isolate when there are mitigating circumstances that mean isolation should not be necessary. However, there is no recourse to appeal so once an instruction to isolate is received from the App, the phone user potentially becomes liable to a significant fine should they ignore the diktat.

At the very least the app needs to be capable of saying something like “you were in this place on that date between this time and that time and it is now necessary for you to isolate because people carrying an infection were in proximity at the same time. If you disagree with this information, please contact... or click here.”

This would enable the phone user to verify for themselves the data on which the instruction was based and appeal if they believe the instruction is unjustified. If the App did that it will be a useful tool, instead of being a potentially erroneous and harmful intrusion into the user’s liberty.

It seems unlikely the App will be improved in the short term, especially as privacy is being cited as a reason why more information cannot be shared with those who are instructed to isolate. In the meantime, anyone installing the App needs to be very aware of its shortcomings and the potential “gotchas” (false positives) that it might generate. The more cautious might be well advised not to install it, or at least switch off Bluetooth when they are in locations where erroneous results might be generated.


It has emerged that an instruction from the NHS Track and Trace App to self-isolate is not enforceable, because the data / process is not of sufficient reliability and robustness to withstand legal scrutiny. This then raises three further questions:

1. If the data is not reliable, why has the App been introduced - and how many false isolation instructions will it issue?

2. If the instruction from the App to self-isolate is unenforceable - and users are aware of that - how many will just ignore it? Does it not undermine the whole point of the program?

3. If the data is questionable, surely sharing the data with those affected would be a means of enabling them to assess for themselves whether the instruction is appropriate to their individual circumstances.

© Andy Martin 2020

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