Update to NHS COVID-19 app brings improved warnings, end to 'ghost' notifications The NHS has updated its COVID-19 app for England and Wales*, meaning it now uses the latest version of the contact tracing API co-developed by Google and Apple. Like all apps using the Google-Apple Exposure Notification (GAEN) contact-tracing APIs, NHS COVID-19 uses Bluetooth handshakes between devices to identify the duration …
>Medium proximity, which is defined as between two and four meters (6.5ft to 13ft), is scored at 150 points. Previously, you needed to rack up 900 points in order for the app to issue a self-isolation warning. Now, that's been reduced to 120 points.
So, standing in the next aisle in a supermarket to a person who tests positive despite being separated by a barrier over two meters high will land you under 'house arrest'? Isn't that a rather low risk situation to convert into "thou shalt self-isolate for 14 days'? And they expect people to volunteer to use this.
The details the make it into the story don't include the time limit. 13ft is almost exactly 4 metres. It's unclear from any of the linked articles what exactly the points system is, and strikingly the 120 point limit is below the amount of points awarded for the lower exposure, so why have the threshold?
No doubt this is all calculated somehow, they may weight the points based on the filter output for example, but have a look at the only article referred to that mentions the points change (I'm being generous, it's a link off a referenced article), https://healthtech.blog.gov.uk/2020/10/29/how-the-nhs-covid-19-app-is-making-the-most-of-cutting-edge-global-technology/
Now, I've not spent 15 minutes in a shop queue for a long time, yet I got the low exposure notification warnings. So where is the guarantee that walking down the street isn't enough to trigger an isolation warning without sight of the scoring system?
Back in April (and into May I think) the queue for our local post offices was about an hour long. The big supermarkets I took to timing, and generally about ten minutes, but was longer if you went at the wrong time. Now we're back to supermarkets being crowded and no distancing, which means you're not likely to be next to one person for 15 minutes, but probably doesn't make it any less likely for a carrier to pass it on, just that you'll have no idea who to.
But it could read 2m as 4m, which is above the warning threshold. Of course, in that specific circumstance it's unlikely you'd be that close for that long, whatever the time limit is that the app/back-end is basing it on, but there are other circumstances where you may well be close to someone for that long, even though separated by a barrier of some sort. eg sitting 2m away from someone at work, facing in opposite directions or even separated by a perspex screen.. The scoring threshold does seem to be a bit low, and as has been mentioned is not helpful if we don't know for sure what exposure duration is being used.
"So, standing in the next aisle in a supermarket to a person who tests positive despite being separated by a barrier over two meters high"
Aalto University did a computer model of a cough in a supermarket aisle - over the course of 6 mintues, the droplets spread *over* the aisle divider and into the next aisle (aided by the AC system, I assume).
https://www.youtube.com/watch?v=WZSKoNGTR6Q
I would want to know if I had spent 15 minutes in a queue with an infected person _in the same store_. Then I would absolutely not go to my parents to fix their broadband for at least a week, would not go to collect click and collect items, etc. Without making more of an effort to contain spread, we will still be going in and out of tier 2 in 6 months time.
Ian Mason,
It's hard to tell, because of journalism's general scattergun approach to reporting (and to be fair the massive number of Covid research papers that come out every week) - but I believe that thinking is changing on Covid-19 to the idea that more of the spread is due to aerosols and less to droplets and touching surfaces. If that's true it would explain why they're lowering the proximity threshholds. Although it might just be from more experience of operating the app.
They've probably got a model that says if x number of positive tests, and y number of people are using the app - then we should be getting z number of people being asked to isolate by it. And if that's not happening then you change the app. Plus presumably other governments will be sharing whatever threshholds they've set - so everyone can tweak it.
Why is it so hard for people to understand that there is a difference between 'not working perfectly' and 'not being useful'?
Any method of evaluating whether you have been exposed to enough of the thing to infect you short of actually directly detecting an infection is going to be only statistically useful and subject to both false positives and false negatives. And it's trivially easy to invent both cases for something like the BT thing – stand the other side of a closed window from someone who is infected for an hour and you'll get a false positive, stand for an hour next to someone who is infected in a sufficiently electrically noisy environment and you'll get a false negative. That doesn't mean the tool is useless. It may actually be nearly useless, but these things don't show it is.
Certainly, given the current thing seems to be pretty good privacy-wise, people refusing to use it because there can be false positives and negatives and fals positives might slightly inconvenience them are actively helping to make it less useful and thus increasing the risk for everyone, in just the same way anti-vaxxers do (vaccines, of course, are also only statistically effective). So thanks for that.
And in the concrete case you suggest, well: if I'd stood that close to someone infected in an enclosed space where the air conditioning is busily circulating the air around and where there's not an airtight barrier for long enough that the system thought I was at risk then, actually I'd kind of like to know that before going to visit my elderly relatives, because I'd rather be very sure indeed they didn't die because of me. Because, you know, I care about other people.
In fact even the ghost alerts were kind of useful. I live in a fairly small town where, given estimated current infection rates in the region, we'd probably expect no-one to be infected. I got a ghost alert the other day: so now I know that there almost certainly is at least one person known to be infected here (it might have been a passing car), and that's kind of a useful data point.
If being within 4 metres of an infected person for 15 minutes scores 150 points, how many do I get for being within 4 metres of three different infected people at, say, 4-hour intervals for 5 minutes each?
Also, does anyone know how much signal attenuation there is through glass? For example, would sitting by a window in a café or pub give you points from an infected person on the other side of the window?
One thing that drives me nuts is people posting "me too", "I have the same issue" on an issue (e.g. GitHub) without adding any additional information like a different version number tested or a test case not in the original report.
Not saying that's a reason to down vote someone's El Reg comment but I checked your comment history and your "discovery" of this issue was not downvoted, it was your accusation of another commentard as a racist.
I live in one of the lowest incidence areas of the UK.
The whole county had 11 new cases yesterday. My actual town had 0 to 2.
Yet the app reports my risk level as HIGH. My guess is that it is using the fire break status to report risk level rather than actual incidence. Are there risk levels higher than HIGH? Like VERY HIGH?
The government in England have gone for a coffee chain approach to risk. In coffee shops you can have medium, large and extra large - there is no small. Similarly in England we have 3 tiers of rules medium high and very high. There is no low - which is presumably some phychobabble about not wanting people to feel too secure and stop taking precautions.
I would assume (though it doesn't say on the Government site) that low risk means the rules as we had them over the Summer. Medium is then pubs and restaurants closed by 10 and only groups of 6 people, then going up to the higher more restricted tiers later.
I missed the fire-break status when reading your post and so didn't realise you were in Wales - that was the only clue in your post. However because I didn't know, I made my answer specific to England, because those are the only government rules I've bothered to read - seeing as they're the ones that apply to me.
However if the civil servants in London are advising ministers not to use Low risk anywhere, it wouldn't surprise me if the ones in Cardiff aren't doing the same thing.
The justification on the NHS app for us being Medium risk a few weeks ago, when we had about 25 cases in the whole county, was that there were bordering councils with higher rates. Which I suspect is just a wording choice to avoid having any low risk areas.
In coffee shops you can have medium, large and extra large - there is no small.
Not on the menu, but if you know the secret you can get one in Starbucks. Whether you want a small Starbucks is left up to the reader.
This post has been deleted by its author
For testing the Beta software so that I don't have to.
I'm still waiting for good quality news reports quantifying how many people have been correctly identified as at risk, then processed by the track and trace (and isolate?) system and successfully quarantined with all their contacts also traced. Plus those in need being given immediate financial support to enable them to self isolate and still pay for food, accomodation, heating etc.
Until then this just seems, to my cynical mind, to be an exercise in magical thinking. We have an App. Problem solved!
Seriously, so far I haven't seen any articles quantifying the benefits that this App has produced. Apart from financial ones for the developers.
England and Wales seem to be drifting into another massive surge in new infections. How is this App helping to limit this?
Mind you, I haven't seen anything quantifying how Scotland and NI are making gains from their systems either.
There must be some obvious benefits or why are we doing this?
I seem to recall some figure like only 28% of people who are supposed to self isolate actually do. So this is surely the area to focus on.
It reminds me of governments' love of passing new legislation to make something illegal and claiming that they have fixed the problem, when there aren't enough police to enforce the law and anyone charged has to wait 2-3 years to get processed by the massively under funded and under resourced court system.
So you install the App and get a notification. Then what???
{and BREATHE}
It doesn't solve the problem, but it does patch up the difficulty of otherwise untraceable contacts. I can tell you who I shared an office with (working from home makes that quite easy...), but not who I shared a queue with.
Here's a nice graphic to help explain why even if something is not a magic bullet it is still worthwhile in our current situation.
https://www.pslhub.org/learn/coronavirus-covid19/tips/the-swiss-cheese-respiratory-virus-pandemic-defence-r3379/
Defence in depth, useful in IT, useful in public health, generally useful in most large numbers games.
I can't find a thorough assessment of Stop Covid NI effectiveness, but they do occasionally mention numbers: https://www.health-ni.gov.uk/news/stopcovid-ni-app-compatible-tracing-apps-scotland-and-jersey
“Since the launch of the ‘StopCOVID NI’ app in July almost 490,000 people have downloaded it and over 20,000 people have been contacted via the app to let them know they have been in close contact with someone who has tested positive for COVID-19. This is allowing people to self-isolate quickly if they have been exposed to the virus, reducing the risk of them infecting others.”
It is nice to see that the biggest companies in the world can work together on the Linux kernel. Apple and Google can work together on this back-end. Yet Scotland and England can't work together on the public facing app. World beating? More like head beating on desk.
I took it off the works phone about two weeks ago due to it sounding alarms in the early hours of the morning.
Upon checking the screen it read that I had been in close contact with someone who had covid 19, upon logging in to the phone there was no such message there.
I have no faith in buggy software and even less in software that is now claiming to be "fixed".
Why have the NHS staff, Police, Fire Service and Ambulance staff been ordered to remove it from their phones if this is the bestest tracing app in the world according to our PM Worzel Gummidge?
What you describe sounds like one of the "ghost notifications", apparently (so we've been told) unavoidably triggered at the API layer, but not meeting the threshold for the NHS Covid app to give you a warning.
I say "apparently", because it's now going around that the warning level for the NHS Covid app had incorrectly been set much higher that intended, so it's quite possible that these host notifications should have been triggering a warning. Came to elReg today to see if they've covered it yet...
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