Originally Posted by corporate-wage-slave (Post 33171064)

Just to illustrate this, if you are testing 100 people who are positive, there is an assumption that 99% of PCRs will come back positive. With LFD the figures vary somewhat by studies, but at worst it's 50%, at best it's 75% come back positive. If people do repeated tests and get good at doing the tests you probably do get to around 70%. It gets to 95% if that cohort is clearly symptomatic, which is the main basis of asking for a PCR. But missing half of positive cases as well as not tracking variants of concern is just a step too far at the moment, when you add in a domestic context where some of the more stringent lockdown rules are being relaxed in England and Wales.

The slightly more complicated aspect to this is we tend to assume PCRs are 100% accurate and therefore base LFD accuracy alongside this. We have found a very small number of cases which were positive on LFD, negative on first PCR and positive on a second PCR, so it's probably 97-99% accuracy for PCR.

Just to further complicate this, there is a little bit of evidence that asymptomatic cases are rising as a proportion of cases (which are otherwise falling in total number in the UK). The often quoted 30% seems now too low, it may even be as high as 50%.

Originally Posted by itisme (Post 33171163)

Not completely on-topic but there isnt another topic covering this.
The rules in UK state: hotels are open for work-related travel and some government-approved exceptions to support the stay-at-home guidance BUT what's the reality? Will the hotel check why you are staying? Has someone been asked? If booking on a personal account/creditcard do you get asked? Or are they just happy for the revenue and is it a 'don't ask don't tell' policy at the moment? SO many are open from a quick search surely they can't be all full with work-related travel only.

Thx!

Originally Posted by corporate-wage-slave (Post 33171126)

OK, I think that's jumbling a lot of things together. But firstly the twice vaccinated hikers of the Hornstrandir are sufficiently small as a demographic that very little policy is being made with them in mind. The demographics that worry us most are friends and family travellers, who probably constitute the main group travelling now. It's very difficult to stop, when you consider births, deaths and marriages. It's interesting to note this group has acquired a higher priority than leisure travellers, out of sympathy, but ruthless public health policies would permit lying on a beach, prohibit going to funerals. That isn't going to happen, but these people are mixing more intimately than the other extreme, road hauliers, who have just about the most solitary profession going. Britain is nothing like 100% self sufficient in medicines, food, oil products, pet food, vaccines, you name it. Hauliers as a working group are in short supply across Europe, and middle sized haulage companies will simply choose to work elsewhere on the mainland if you make things too difficult to travel to the UK.

Pragmatically you therefore let things slide with some groups until something better arrives. The big deliveries of LFDs happended in March, so again pragmatically they - and cabin crew - can now get ready access to LFDs, and indeed judging from this thread, these LFDs have now been rapidly distributed to the wider community, which is great to hear. This is a very different situation compared to say 6 months ago when even members of the National Security Council were denied access to tests. In the ideal world you would do something like LAMP testing at every port worldwide for all inbound travel, but in the absence of that LFDs will probably do, so long as when people get back we can PCR and genome sequence travellers. Hauliers and cabin crew will get PCR tests, again pragmatically, at least if they have a positive test they can then be PCR'd. There is a separate PCR system for hauliers already in place at TruckStops, so it's not quite as black/white as you portray.

Originally Posted by cauchy (Post 33171166)

Isn't the selling point of the Lateral Flow tests that they're good at detecting people who're clearly infectious, and opposed to merely infected (and mildly or not infectious)? For example, https://www.ox.ac.uk/news/2021-01-21...ld-allow-safer :

Also, in terms of genetic sequencing, I thought this only happens if the Ct value of the PCR test is below 30? We might expect the lateral flows to miss out more of what would be high Ct value cases, but these were never going to be sequenced anyway. The lateral flows ought to be better at what would be lower Ct values. And of course if a lateral flow is positive a PCR can be run and sequencing if appropriate. So how many samples do we miss out on?

Originally Posted by corporate-wage-slave (Post 33171064)

Just to illustrate this, if you are testing 100 people who are positive, there is an assumption that 99% of PCRs will come back positive. With LFD the figures vary somewhat by studies, but at worst it's 50%, at best it's 75% come back positive. If people do repeated tests and get good at doing the tests you probably do get to around 70%. It gets to 95% if that cohort is clearly symptomatic, which is the main basis of asking for a PCR. But missing half of positive cases as well as not tracking variants of concern is just a step too far at the moment, when you add in a domestic context where some of the more stringent lockdown rules are being relaxed in England and Wales.

The slightly more complicated aspect to this is we tend to assume PCRs are 100% accurate and therefore base LFD accuracy alongside this. We have found a very small number of cases which were positive on LFD, negative on first PCR and positive on a second PCR, so it's probably 97-99% accuracy for PCR.

Just to further complicate this, there is a little bit of evidence that asymptomatic cases are rising as a proportion of cases (which are otherwise falling in total number in the UK). The often quoted 30% seems now too low, it may even be as high as 50%.

Originally Posted by Dan1113 (Post 33171194)

could it be that they are rising more because so many people are doing tests now at home on a regular basis, meaning they're catching it before they become symptomatic - so more pre symptomatic rather than asymptomatic?

Originally Posted by itisme (Post 33171163)

Not completely on-topic but there isnt another topic covering this.
The rules in UK state: hotels are open for work-related travel and some government-approved exceptions to support the stay-at-home guidance BUT what's the reality? Will the hotel check why you are staying? Has someone been asked? If booking on a personal account/creditcard do you get asked? Or are they just happy for the revenue and is it a 'don't ask don't tell' policy at the moment? SO many are open from a quick search surely they can't be all full with work-related travel only.

Originally Posted by Schwann (Post 33171197)

If the government wants everyone to be tested for variants after arrival, would it not be advisable to keep those tests within the remit of the existing NHS Test & Trace infrastructure? No idea what the cost to the NHS is for processing and sequencing a PCR test kit, but I would rather pay cost or to profit to the NHS T&T budget than paying £100 to Beautiful Brows or whichever company has decided to cream off profits from suddenly becoming a test provider.

Originally Posted by corporate-wage-slave (Post 33171199)

Yes, that's probably part of it, but the virus - and the virus' victims - have changed behaviour over the course of the last year. We know, for example, that B.1.1.7 is slightly backloaded in terms of symptoms timeline compared to vanilla Covid. Plus there is still a lot we don't know about the virus, even now.

Originally Posted by chimichanga (Post 33171228)

corporate-wage-slave On Reddit, I've been reading that supply of 1st dose vaccines will plummet from currently around 100k per day to close to zero from next week. Is that also what you are seeing in your data? I believe they advise you on the expected deliveries a few weeks in advance, right?

Originally Posted by paulaf (Post 33171249)

Whereas DM reporting this:

Covid UK: People in their 40s will be invited for jabs from tomorrow https://www.dailymail.co.uk/news/art...ticle-masthead