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Enteleon - way beyond anything I can speak to with confidence. An antigen test would be a useful first pass at picking up positive results, but an RNA sequence would be required to determine if the virus mutates into a number of strains.
If this virus does mutate, affimer tech would put Avacta's test in the driving seat again, with their proven ability to be fast to market. Silver linings...
ST,
You didn't have to strawman me with "all your alleged diplomas", that wasn't based on anything I said... It's interesting you chose to take that angle.
If you'd refer to the text of the comments from PL and myself I tried to do exactly that but the guy still doesn't believe that this test is capable of producing FPs, or that they would be relevant in any case, and is therefore mana from heaven. I'm prepared to wait for the outcome from Avacta regarding performance.
You can keep grinding on about one sarcastic comment if you choose, but I'd rather get on with my life. Filtered.
GG
@ST, it's a shame you feel that way. One tongue in cheek comment and you're off on the anti-intellectual express. I'm claiming absolutely nothing other than a basic understanding of how this test will be evaluated.
And yes, Ol' Buffett has rather spoiled his reputation lately, but a more appropriate legendary investor didn't readily spring to mind. I'm sure you understood the spirit of my statement
In that case your question sounds like a determination of PPV - the likelihood that a positive result is a true positive. All other things being equal the PPV goes up the higher the prevalence of the infection in the population.
For a worked example of PPV I'd refer you to abdalian's post at 11:16 that they got slated for. I'm not sure if their numbers are completely reflective of the current COVID19 reality, but they seem accurate as far as the calculation goes
@enteleon I'm no oracle here, but pretty much what PL75 said - The test is designed to confirm presence of antigens, not a clinical diagnosis. If the person is at the peak of their infection, they may not have antibodies. Two weeks later they may. I may test negative for antigens early in the infection, I may test positive a few days later. At various stages of infection the serum/saliva levels of targets will vary.
The test will have a Limit of Detection. The test's validated capabilities will inform the user about the extent to which a negative is 'a true negative, or the sample is below testable concentrations of the target'. This could be translated into a marketing description of validity such as "5 days before, 10 days post symptomatic onset" (for example)
Wolfie - agreed. I doubt there will be total focus on any one market, so the rules of one particular regulator aren't too important. I only mentioned FDA approval as a relatively low bar to clear given the recent relaxation of the test requirements in light of the ongoing emergency.
@Ophidian thanks for the correction
And I agree, I hope I haven't gotten my point muddled. I believe that the affimer platform and pre-LFT work has shown that the S&S should be well above what is required, and far beyond what most competing tests can offer. However, that remains speculation until confirmed by Cytiva/Avacta. And for people with below-detectable levels - Avacta should only be worrying about what is possible to detect. It's science, not magic.
My main point of contention is people brazenly stating that "it doesn't matter if a test produces loads of false positives".
@WolfieBill FDA guidance on COVID19 tests: "Tests should accurately identify at least 90% of positive cases (sensitivity) and 95% of negative cases (specificity)".
These just aren't reasonable parameters for whole population screening. On a scale of 65 million tests (UK only) these figures would authorise a test that could find 3.25 million false positives
I don't really understand what you're trying to say in your last sentence, but from a marketing standpoint a company will sell a test on the basis of its quality, not just that it's been approved (assuming that your audience knows the difference). If a test is marketed direct to consumers, most uninformed people will assume that the result is completely accurate. If you're selling to a Government, or a huge corporation, there is due diligence involved, and often a tender process which really scrutinises the contract. Selling a test that doesn't perform as well as other available tests means you will have no large customers.
Chengdo4 evidence of what? Do you think I have access to the in-house results from Avacta relating to their IP, or perhaps early access to the next RNS? I'm waiting just like you.
If it's broad strokes about what defines sensitivity/specificity/PPVs, pick up a stats 101 text book. Or if you've got an hour to kill maybe try geekymedics .com/sensitivity-specificity-ppv-and-npv/
I'll give you an example you might relate to better, as you clearly don't have any understanding of the biological or epidemiological merit.
If we're looking for strong investment choices, a punter with high sensitivity and specificity finds ALL the strong investments and never strikes out. That's a Warren Buffett. If you have a high sensitivity and low specificity, you'll throw money at anything that catches your attention, whether or not you should. That's 95% of LSE
@tomvisual - yes and no. The lab results confirm that the affimers are highly specific to the exact antigen presented by SARV-COV-2 (the spike proteins). To the best of my knowledge they haven't confirmed anything thus far in terms of how well that is picked up from a natural saliva sample, which will have all kinds of other gunk in it, or how well it performs on a test strip. That's the next big RNS, as Cytiva are seeing to that side of things
No, you're right PL75. I'm only a statistical biologist so I'm sure you know antigens vs antibodies better than I do...
I'm telling you for a fact that any false positive is inherently a bad result, and that means the test doesn't work well. Avacta isn't aiming to create a bad test, it's aiming to take the best the lab can provide and put it in your pocket. If it can't do that, this SP will sink like a stone, because all the short term holders that only know about a COVID19 test will leave in a rush.
I just... can't... understand your perspective here. Is there a sane reason that you think a test producing a high rate of false positives is a good thing?
And yes, FDA approval numbers are a low bar, but it's a competitive market. Having FDA approval means Avacta/Cytiva can sell a test, it doesn't mean anyone would buy it
PL75 do you think this company is going to carry on shooting for the moon with a test that has low specificity? We're banking on this test becoming a first choice diagnostic device as it has speed and resource benefits over the gold standard, almost 100% sensitive and specific laboratory tests.
No company or government are going to shift from current testing best practice to Avacta's test if it produces a large number of false positives. That makes it a bad test, and it will never go to market.
If the crucial question is "do i have this virus" and the test isn't sensitive, the answer isn't yes or no, it's Maybe, and that helps absolutely nobody
I'm not sure why posters here seem to have a negative response towards pure statistics. By my reckoning Abdalian's comment is correct and correctly identifies the problem.
The positive out of this is that a) infected persons exhibit high viral load in saliva b) these affimers have already been demonstrated to have an incredibly high specificity per the RNS (even with decoy targets which are very closely related viral 'species') c) this test is for antigens, which has a clear role in infection, whereas antibodies don't seem to have a confirmed role in long term immunity. All the right pieces are in all the right holes.
Just please be aware that when someone presents statistics and you 'doubt' them, you lose all credibility as an informed voice
"Why is a false positive an issue for an antigen test?" - surely this is a joke?
"If one person in the UK is infected and you test all 65M and get 2 positive results, one true and one false, that does not mean the test has produced 50% false positive results" - this is what positive predictive value is. It means "how likely is my positive to be really positive". Abdalian's analysis is correct based on the numbers they provided. For the numbers you provided the specificity would be 99.99999985%, which again, agrees with the "specificity of the test needs to be pretty much 100%" as stated below
In response to that I would only say this: currently life is not normal, and the reason is that any attempt at mass gatherings would spring a second wave. The COVID19 detection tests won't be late to the party if they come after the peak of infection, they'll only be late if other providers satisfy the niche first, with enough capacity, speed, sensitivity, and specificity.
This is a product that is required for civilisation to resume, if you think the ship is sailing be grateful many of your friends or family aren't furloughed, because I hear the message every day that we are on hold as a society.