Boris's Brain is missing

[Psamathe]

Today we have street by street tests in some places because of the SA variant but travellers can still arrive from SA without either tests or quarantine.

Street-by-street tests make it really look like the Government is "doing something". Quietly ferrying people airport to quarantine hotel is largely hidden from view. We have a leadership that is now more concerned about how they are perceived than actually taking advice so meaningful action just doesn't happen.

Another example is Johnson's failure to follow his own "stay at home" message - because rushing all ver the country for perpetual photo opportunities impacts how people think of him despite it being completely the opposite of the message he is forever repeating (it's "do as I say not as I do").

Ian

[Ben@Forest]

Today we have street by street tests in some places because of the SA variant but travellers can still arrive from SA without either tests or quarantine.

South Africa is on the list of countries on which there is a travel ban. You can only come in from South Africa (similarly a whole host of southern African countries) if you are a British or Irish national and then you are required to self-isolate for 10 days.

[Jdsk]

Today we have street by street tests in some places because of the SA variant...

One side-effect of this might be that the UK is about to see what effective testing, tracing and isolating looks like. It's been missing so far and people genuinely might not know what it can achieve.

Jonathan

[Oldjohnw]

You can get here from SA by circuitous routes. Pre travel testing and airport arrivals quarantine should be universal.

[Psamathe]

Today we have street by street tests in some places because of the SA variant...

One side-effect of this might be that the UK is about to see what effective testing, tracing and isolating looks like. It's been missing so far and people genuinely might not know what it can achieve.

Jonathan

What sort of tests are they operating door-to-door? I'd be concerned if it's the lateral flow given the (un-)reliability and false negative rate. On a population screening basis I see they can help detect asymptomatic cases that would otherwise just be spreaders. But the risks of false negatives changing people's behaviour where you are apparently trying to stop a particular variant could be problematic i.e. allowing e.g. 1 in 3 SA variants through and adding "change of behaviour" to a %age of those might more than counter the detection of asymptomatic cases. Add the lack of support for those isolating (e.g. loss of earnings) and the lack of enforcement ...

Of course if they are the PCR tests then above not applicable..

Ian

[Psamathe]

You can get here from SA by circuitous routes. Pre travel testing and airport arrivals quarantine should be universal.

I would agree. Often more indirect routes to/from more distant places can be cheaper (though I don't know about South African flights and don't know about flights during the pandemic). Particularly "cheaper" when a direct flight also involvs an expensive quarantine hotel at the end!

Ian

[Jdsk]

Today we have street by street tests in some places because of the SA variant...

One side-effect of this might be that the UK is about to see what effective testing, tracing and isolating looks like. It's been missing so far and people genuinely might not know what it can achieve.

What sort of tests are they operating door-to-door? I'd be concerned if it's the lateral flow given the (un-)reliability and false negative rate. On a population screening basis I see they can help detect asymptomatic cases that would otherwise just be spreaders. But the risks of false negatives changing people's behaviour where you are apparently trying to stop a particular variant could be problematic i.e. allowing e.g. 1 in 3 SA variants through and adding "change of behaviour" to a %age of those might more than counter the detection of asymptomatic cases. Add the lack of support for those isolating (e.g. loss of earnings) and the lack of enforcement ...

Of course if they are the PCR tests then above not applicable..

It's PCR in Woking, and I imagine the same in the other locations.

And all positives from all of the affected locations will be sequenced.

Jonathan

PS: You're right about the general problem of inappropriate reassurance with low-sensitivity tests.

[PDQ Mobile]

It is extraordinary, this widespread travelling.
At the time 2000 lorries and their largly self isolated drivers were stopped from crossing the Channel for days, something like 20,000 people went skiing!! Mostly by plane.

Some of them subsequently fled an imposed quarantine in Grenoble.
I never did hear where they went or how they got back to the UK?

If there is a dangerous mutation in a given place one would have thought keeping it isolated there would be a priority?
There are parallels to the first months of this in this report about China.
https://www.bbc.co.uk/news/world-55756452

Some of us would like to travel but don't because we feel it irresponsible.
Others see themselves above any restrictions even for a holiday.
Stanley Johnson springs to mind.


Anyone hazard a guess at groupings that feel themselves above the law?

[Psamathe]

Not only was his trup to Scotland un-necessary (and thus against his "essential only" and stay at home guidance and against Scottish law) but he also visited a site going through a C-19 outbreak, had been warned about it before his visit and ignored those warnings:

Boris Johnson accused of putting ‘politics above public health’ after visiting vaccine plant during staff Covid outbreak
Boris Johnson visited a vaccine plant despite No 10 being warned of a Covid outbreak, triggering condemnation in the Commons.

The prime minister was accused of a “reckless PR stunt” – after it emerged that the boss of the plant in Scotland had alerted his team to the outbreak.

“The prime minister and his advisers knew there was a serious Covid-19 outbreak at this plant – they knew the visit posed a risk,” SNP Westminster leader Ian Blackford said.

The visit, to the Valneva factory, in Livingston, was made last Thursday, on Mr Johnson’s ‘Save the Union’ trip north of the border.

Valneva’s chief financial officer, David Lawrence, has said that Downing Street had been informed ahead of the 14 coronavirus cases at the plant – about one in eight of the workforce.

Ian

[Tangled Metal]

Isn't the issue with lateral flow tests that they're used for inappropriate circumstances and not for a public health application where it's ability to be more accurate for catching people shedding the virus than all positives is used?

Something like that I think the expert running liverpool's mass testing mart year said.

[Jdsk]

I don't understand the first sentence.

An assay with a high rate of false negatives can be useful, it depends on what you do when you have the result.

Jonathan

[Psamathe]

Isn't the issue with lateral flow tests that they're used for inappropriate circumstances and not for a public health application where it's ability to be more accurate for catching people shedding the virus than all positives is used?

Something like that I think the expert running liverpool's mass testing mart year said.

My (maybe incorrect) understanding:
These lateral flow tests are very prone to giving a false negative result (i.e. saying "you're clear when reality is and PCR says you have virus). I understand that out of 10 people with C-19 the lateral flow can say as many as 4 of that 10 are clear (although rates vary depending on who is doing the test).

Thus, for e.g. testing a visitor prior to visiting somebody in a care home these tests would be a disaster, allowing up to 4 infected people to visit for every 10 tested!

But for community scanning where you want to detect asymptomatic cases to get them to isolate, you can regard the test as detecting 6 out of 10 cases (at worst) that would not otherwise be detected.

But research shows that if you tell somebody they are clear that can change their behaviour (i.e. some do go and visit aged family who are shielding) - even though there is maybe a 4 in 10 chance the result was wrong! Apparently if you give them a bit of paper saying "you're clear" the behaviour change is more likely and less "social distancing". This was from Prof Steve Reicher on C4 News some time ago (so maybe a search of C4 News clips might give a source).

So, for population scanning, you have to balance the risks of the unreliable test encouraging more risky behaviour vs detecting asymptomatic cases and getting them to isolate. And it gets even more complex as inadequate Government support for those in need make self-isolating difficult. Thus those in less well-off areas, higher housing density, maybe mixed generation households are less likely to come forward for population scanning as there is a risk they'd be forced to self-isolate which they cannot afford to do (lost income, inadequate Gov. support).

(If my understanding is incorrect, please anybody feel free to correct it).

Ian

[Jdsk]

I'd add one bit...

The false-negative rate isn't an inherent property of the assay in the same way as specificity or sensitivity. It depends on the true prevalence of the condition of interest.

Jonathan

[Psamathe]

I'd add one bit...

The false-negative rate isn't an inherent property of the assay in the same way as specificity or sensitivity. It depends on the true prevalence of the condition of interest.

Jonathan

The 6 out 10 to figures I've seen were phrased as, put 10 samples with C-19 virus into the test and 4 will say clear 6 say virus.

The rapid test kits most widely used in UK universities, schools, and care homes detect just 48.89% of covid-19 infections in asymptomatic people when compared with a polymerase chain reaction (PCR) test, real world data from the Liverpool pilot have shown.

Ian

[Jdsk]

Yes, that might be right for the prevalence in that population at that time. But it will be different in a population with a different prevalence.

You can explore the effects with the BMJ interactive calculator:
https://sandpit.bmj.com/graphics/2020/c19test/

Jonathan