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You keep saying sensitive. It’s irrelevant for confirming positives.
You have a 100% sensitive green light test. It’s called affidx, if you’re negative you’re 100% confident you’re negative so you’re green to go. It’s 99.x% specific so there’s a chance you might be a false positive....
You get a positive result. You need a red light test to determine if you should isolate. To confirm you use an LFD that’s 100% specific, possibly innova. If you’re then negative you can be confident you’re negative, if you’re positive you get a PCR for variant tracking. You should isolate as the chances of two false positives are minuscule as you’ve taken a 1 in 1000+ and a 1 in 10000 test.
That’s all I’ve got, I can’t explain it for a fourth time.
Although playing devil’s advocate to myself, the benefit of including the an test in this process might be earlier confirmation of the most high viral load cases, which could help to also accelerate contact tracing.
Harder to say if there would be an economic benefit, because for every case where you save a PCR test there will probably be a few where you run both PCR and a second LFT.
Agree with Infinis on this. Think about the process:
- Run AffiDx
- Negative: green light
- Positive: run N protein test
- N positive: red light, isolate
- N negative: order PCR confirmation, meanwhile isolate
- PCR positive: red light, isolate
- PCR negative: green light, release
If you have to do the same thing no matter what the N test outcome, it’s pointless, and you might as well go straight to PCR for confirmation.
Alternatively if you require a positive on both tests, you lose the benefit of the AffiDx sensitivity.
The consequences of a positive result are quite severe (self isolate for 10 days), so even if 99.9% specificity, why not just validate with a 2nd, different tech/target LFT (cost of +/- £5) to rule out the false positive?
If the Gov are faced with a choice of Sensitivity vs specificity then its a no brainer to select most sensitive and back it up (rule out false positives) with a validation/back up test.
Positive/Positive = Self Isolate
Positive/negative combo should be checked via PCR = self isolate until checked via PCR
They have to select the most sensitive test as the primary. Would make zero sense to select a less sensitive test and miss a high % of infectious. Which means, imo, AVCT has to be selected as the primary Sovereign test.
Its about the functionality of a back up - ideally it should tell you whether or not the positive on the first test was indeed a positive or was actually a negative so decisions about isolation can be made. Only a test with very great sens and spec can perform that function properly
If you are just using those backs ups to confirm positives are positives then fine. But if the back ups suggest you are negative when the Affidx says you were positive then you would need to be treated as a potential positive still and only released once a super sensitive test says you are negative. Given that I don't see a materially enough useful function for the back-ups to warrant them being employed - especially as with the public they carry the danger of being treated as a green light where they return a negative.
You've just mentioned sensitivity again. The chances of being positive on 2 tests that target different proteins and if both have specificity of 1 in 1000 to 1 in 10000 then yes, I'd absolutely trust it. The sensitivity is to confirm you are negative, so you're not ruining anything. If you're negative on an AffiDx then you're 100% not infectious. If you're positive, you need confirmation, so why not use another LFD? If anything it's a better option than PCR as that can give you a false 'positive' at a high Ct that is just residual virus.
what I mean is if you release those 27-30 folk because even though Affidx says positive one or more of these less snesitive tests says negative then you risk actually releasing infectious folk
If you had a positive Affidx and then a second test Innova said you were actually negative could you trust it? Absolutely not. And for surescreen and Mologic? Still couldn't really trust it. Basically by following up with less sensitive tests you ruin the whole point of a very sensitive one which is to pick up even the positives for folk with lowish viral loads that could still be infectious e.g. you 27-30 CT range folk.
Why? Specificity is what is important for verifying positives. If the most convenient and fast way that avoids isolation is another LFD rather than needing to book a PCR test then why not?
I don't like the strategy of determining whether a positive is positive or not with a less sensitive test. Go to PCR or BAMS if you want release and try and limit their turnaround times. Most people can withstand a wait. Where timing is critical e.g LFT positive on morning of flight - then find a bespoke solution to get ultra fast turnaround - maybe even PCR labs on the edge of airport sites or some sort of accurate mobile PCR or BAMS
I hope the offer AS has submitted to the UK Gov is valid until COB today. If not accepted by COB today, the capacity we have with BBI, ABDX and MOL/GAD will be sold directly to Europe.
I think we might find out today. Fingers crossed :)
It’s up to the govt and MHRA to sort themselves out. Innova is currently a red light test. We now need the green light test approved and out there. Although, if we’ve already sold everything in to Europe...
Agreed. The specificity issue must be driving AS mad as it’s a blot to be honest. My money’s on the CE being accompanying by further validation numbers to improve that figure.
Fortunately, this isn’t an academic problem to solve, is a logistical one. People want holidays, the football, weddings, work place opening etc. We’d never achieve the ‘beyond zero’ target using PCR.
Perfect can’t be the enemy of good here. Reduce to a point of control. Our test is more than capable of that.
You're right, and that's the beauty of a 100% sensitive test. The complication is from Deeks et al who pipe up if it's not 100% specific when there is low prevalence as it's impossible to have confidence in positive results. You then get the media banging on about people isolating for no reason due to inaccurate LFDs. This solves that problem. Not that there's much of a problem as PCR confirmation is already recommended, but that doesn't stop ol' testicle face.
Thanks.
This process is about detecting infectious people, not detecting the protein. Our test is 100% sensitive in detecting potentially infectious people.
The requirement is for reducing the spread to a point where it’s controlled, using a quick, cheap device. This is a simple, disposable device that does that. No need to over complicate things.
Bein,
No, while 2 x positives with Affidx would increase likelihood of a positive, there could be something that is detected triggering the false positive. If you were to see 2 x positives using 2 x reagents checking for 2 x proteins, the odds of a false positive would be 0% - thus Gov should use the most sensitive test for daily testing and back it up with an alternative test (diff reagent + protein) to validate. This rules out any false positives.
Ask Mina for his view on this.
Or just use two of ours. The solution has no requirement to be equitable, it’s just has to work.
As a UK Sovereign test package (e.g. box of 7 contains 5 x Affidx, 1 x Mol and 1 x Surecreeen) its the perfect home made solution to this crisis. Provide clear instrcutions;
- Affidx - if positive;
- Validate with Mol - if positive self isolate if negative ..
- Validate with Surecreen - and if negative, release as odds of both Mol and Surecreen both missing = very low chance of being positive and if positive, not likely to be infectious.
Can someone get onto the Innovation Lord (Bethell) and tell him we have cracked the challenge?
So what are we waiting for?
The proposed solution would deliver 100% safety and could be deployed (e.g. twice weekly testing for the entire UK pop) at times of very low prevalence (e.g. any positive with AVCT could be validated/rectified via the Innova/MOL test). If you really want to avoid the false negatives, how about;
- Affidx - if positive;
- Validate with Mol - if positive self isolate if negative ..
- Validate with Surecreen - and if negative, release as odds of both Mol and Surecreen both missing = very low chance of being positive and if positive, not likely to be infectious.
You don’t take them both all the time though CO. You take your daily green light test. It’s 100% sensitive so if it’s negative you’re 100% confident you’re safe. If it’s positive, you confirm it with the 100% specific test. If at that point you’re still positive then go get your PCR test. If not, you’re ok to go about your business, but only in a cautiously optimistic way
Sounds like a pretty good idea as an interim solution before the combined test, but hard to know for sure without seeing the direct comparative data. It is possible some people may show up positive on the N test and not the S test. Unlikely at the moment perhaps, and maybe this is one of the development challenges for the combined test! If all the N test true positives are also positive on the Avacta S test, running both would not improve sensitivity. But as you say, a positive on both would give greater confidence of a true result.
I imagine a single positive result (and the other negative) would mean isolate and get a PCR to confirm. Both positive might or might not need PCR to confirm - it would need trials to test though.
For the combined test they’re working on, there is also the issue of harmonising read times, as discussed the other day. Every combination of reagents/test components has an optimum read-time to balance sensitivity vs risk of false positives (e.g Mologic’s “ignore result after 15min” test). So finding something to match the read time of the S test is key. At the moment I wouldn’t be surprised if reading Avacta’s test after 20 minutes gives a better result than reading both it plus Mologic’s tests together after 10.
But one thing’s for sure. Interpreting 3+ lines would be more complicated (if even only slightly), and therefore increase the rate of false results through user error in reading the test. I would imagine a smart phone app being incorporated to read the test, for the set-test version if not POC. Might be the same for the way you suggest here. Any additional complication will increase the rate of user error.
No, you’re not leading the way, I’ve already suggested it except I said they should use up the innova tests for it as they’re pretty much 100% specific and target the n protein. Ours is the green light test - the good guy and the Innova test is the bad guy red light test.
Question - could the 2 tests work together as a package, deployed as separate tests?
Affidx would be the primary test, which would detect the infectious (CT<27) and also very low viral loads that may not even be infectious (CT<31), thus from the sensitivity standpoint, and with focus on false negatives, AVCT delivers 100% of what is required.
Now, if AffiDx detected a positive case, could the Mologic test be deployed as the back up / verification test? If both Affidx (s) and Mol (n) were to detect the positive then the odds of a false positive are surely 0% and the individual should be forced to self isolate - no need for PCR follow up.
Am I leading the way with this idea?