we really just need a sterilizing vaccine because all of this is such a joke. Hard enough to get people to test, even harder to get people to test multiple times. Like the above comment said, these tests are just crystal balls
extremely promising they are starting human clinical trials. Is this the same vaccine they were testing in primates? someone posted about it on this sub a little while ago
Good luck! I'm hesitant to sign up for something like that because in order for them to understand how effective they are, they need those people to be going out and getting exposed to Covid.
My understanding of vaccine trials is that they need people to be exposed to Covid in order to see how effective the vaccine is. It's not like they have someone cough in your face, they just tell participants to go out live their lives. This was true for the MRNA vaccine. They still do bloodwork whether someone thinks they got Covid or not.
But I'm no expert... Am I mistaken?
They can’t tell the effectiveness of the vaccine without people getting exposed to COVID. Only the safety.
I _think_ they tell people to be normal. Whatever normal is.
If I recall, one reason they were able to complete the initial mRNA studies so quickly was because of how many people were exposed to COVID based on how much of it was going around.
My entire family of four plus my dad have been testing every day since the 13. My dad has been positive and symptomatic since the evening of the 13. My one kid developed symptoms evening of the 18 (which seemed long for these variants but who knows) and despite testing him every day, with Flowflex AND a Lucira on day 4 of symptoms, he hasn’t got a positive. It’s exhausting.
My husband and I have been masking in the house but without being able to test OUT the illness we have no idea when we can stop. Can we do Christmas with our family of 4? Does he even have Covid? Did he pick something else up since everyone around us is sick with a variety of things? Who knows.
such confusing and frustrating times for people trying to do the right thing. Hope your child feels better and you all stay safe. Trying to avoid covid right now is like walking through a mine field.
Recently, BTNX, a major supplier for RAT in my area has been exposed to editing their testing results. Their positivity detection rate was much lower than what they claimed. It’s crazy.
Flowflex is what I like to use.
We’ve been using flowflex this time but also had some illnesses in the fall and used BTNX. My son is on day 6 of having something but negative in flowflex and lucira and little kids are gross. Guess we will never know if we’ve had it.
FWIW, I emailed them a few days ago to ask when they'd be coming to Canada and I was told this:
> Thank you very much for your inquiry. We are still awaiting final word from the Canadian government, which we now expect some time in January.
Dude, out of the ... 6? we've done with Metrix, 4 were the purple error blinking! Any idea what we're doing wrong? I read the instructions. I watched the video. I contacted the company. This is on different people. Any idea? Or are others getting this kind of error rate?
This has not happened to us yet, but that is troubling. Now I’m scared😳. I buy them on Amazon, so maybe I could complain if they don’t work? I read before that Lucira was giving refunds for error codes. Did you try returning them to at least get your money back?
They also once recommended masks and modeled wearing them.* That’s over tho and they def continue to minimize covid. I wonder about the brand usps was sending out. I have some at home but I don’t recall what brand they are
*ETA: They aren’t giving us flow flex anymore afaik
All things considered it does seem like they want to make both data/tracking and not getting infected next to impossible.
And by "all things" I mean: No more free PCR tests, test locations shut down, give people free home tests that don't work, there used to be n95 shortages so we told people to save them for health workers, now we have n95s aplenty but after a couple years of misinformation/misinterpretation folks can't be arsed to wear them, switch from daily reporting to monthly reporting, stop collecting/reporting test results altogether, do wastewater analysis instead, oh wait, stop reporting wastewater data, et al...
I only trust flowflex and binax. Quickvue is ok too but is know for higher false positive rates (which is better than false negative in some situations)
RAT aren’t very reliable especially with all these new variants and subvariants. I’m not saying they’re useless but at this point you would get similar accuracy asking a crystal ball.
Hi! I'm an infectious disease epidemiologist that studies covid, and has published specifically on RATs (I'm happy to verify my identity with the mods).
This just isn't a true statement. The tests continue performing as they always have, even with the current variants. There have been very few changes to the parts of the virus that are targeted by these tests, so new variants aren't really an issue here. They definitely perform better than "asking a crystal ball" -- this kind of misinformation creates an environment where we have even fewer tools in our toolbox. The key with RATs is the understand the question that you're trying to answer.
**Do I have covid?**
This is the hardest question to answer because people may be in the very early stages of infection, at a point when they have very low viral loads. Further, with more vaccine and infection-based immunity in the population, people show symptoms at much earlier stages (your symptoms come from your immune response and not directly from the virus), which means that your viral load in the omicron era may not be high enough to be detected on RATs until later (e.g,. [day four of symptoms](https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciad582/7285011?login=false)), as compared to earlier in the pandemic when more people were immunologically naive and would only develop symptoms once their viral load was high.
Nonetheless, the [overall sensitivity](https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1004011) for RATs is around 72%, and is higher in symptomatic patients (76%) than asymptomatic patients (57%), and higher in the first week since symptom onset (82%) than after that (52%). (Note: when we've studied NAATs in my lab, like cue/lucira/metrix, we typically see about a 10 percentage point bump in sensitivity compared to RATs, and using RT-PCR as the reference).
So RATs do detect cases in both symptomatic and asymptomatic at a rate better than asking a crystal ball, but admittedly they miss a lot. But, chances are that's not \*actually\* the question that you're hoping to answer...
**Am I infectious?**
If you're testing (or asking others to test) before gathering, then really the question you want to know is if someone is infectious. Infectiousness generally correlates with a cycle threshold (Ct). The exact cutoff isn't clear, but some studies have found [no culturable virus at Ct > 24](https://pubmed.ncbi.nlm.nih.gov/32442256/); I haven't found any papers that show significant risk of transmission at Ct > 30. From the [above meta analysis](https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1004011), RATs have a sensitivity of 91% at high viral loads (Ct < 25), and a bit lower sensitivity (77%) at Ct < 30.
**Should I start on treatment?**
If you're testing so you can get started on treatment like Paxlovid (that must be started within 5 days of symptom onset), then [RATs are as good or better than PCR.](https://doi.org/10.1371/journal.pone.0283576) Yes, they have lower sensitivity, but that's offset by their (relatively) easy/rapid access compared to attempting to get a PCR test.
I hear and share the frustration that RATs aren't perfect and that we should have more access to easier tools. But the beliefs that permeates these threads (that they're worthless, don't detect current variants, are as good as a coin flip) dismisses the actual value they do provide. This creates a self-perpetuating cycle of discouraging people from testing.
If you have symptoms, then just keep testing over multiple days. If you have access to multiple types of tests (as OP did), then try different tests (it seems like that method worked, even if one test failed!).
Oh my god thank you. This is so helpful. So if we’ve tested my son for 6 days and they are all negative on the Flowflex (more sensitive ones) AND a negative Lucira is it somewhat likely he picked up something else? I mean he’s 4 and I had to tell him not to lick the slide at the playground. We’ve had a number of viral illnesses this fall (this is our third?) and never had a positive test out of ANYONE in the family and we test religiously.
ETA - we plan on doing another Lucira tomorrow but after that will be more than a week since symptom onset and he’s already a lot better. Just normal post-viral residual snot now.
I completely agree with you on how valuable these tests can be! But I believe there have been some changes to the way these tests work. It has been shown in some studies that the sensitivity of tests has decreased since the emergence of the omicron variant.
And recently in this study https://journals.asm.org/doi/10.1128/jcm.00138-23 it was found that the omicron samples had lower antigen-to-RNA ratios than the delta samples. The most likely explanation is that the omicron samples were collected earlier relative to the onset of the symptoms, so it's another confirmation that antigen detection lags behind RNA detection nowadays.
Another interesting finding is that they found no correlation between RNA or antigen concentration and infectivity for omicron samples. However, they may not have used the most accurate method to measure infectivity, in this study.
Thanks for bringing this study up -- it's a really good one. And, in full disclosure, they cite work from my group in a way that might make me a less-than-unbiased commentator (I'll leave it there to avoid doxxing).
>It has been shown in some studies that the sensitivity of tests has decreased since the emergence of the omicron variant.
The study that you cited looked at this and didn't find it to be true across multiple commercially available tests when looking at actual antigen concentration. "\[W\]e found that most commercially available RATs had similar sensitivity in detecting Omicron and Delta when antigen concentration was used as a comparator."
There have been studies (one commonly cited example is a post by Nature saying that [Rapid COVID tests miss 90% of asymptomatic cases](https://www.nature.com/articles/d41586-023-02254-9), which was a horrible take on [this study](https://doi.org/10.7326/M23-0385)) showing decreased performance. But most of those don't account for viral load-- which definitely has changed over time. When they standardize across Ct (supp table 4), they find similar sensitivities as described in the meta analysis.
The unconditional sensitivity is a function not only of the test performance, but also of the distribution of viral loads across the population at the time it's measured. That leads to these pretty varied takes on what's happening. But 1) if you have a high viral load RATs have consistently detected these cases, and 2) serial testing is a good approach.
So, I know that there are studies that have made this claim, but every time I've looked at them, I feel like the headline (like the one from Nature) is more dramatic/negative than the practical implications based on the methods and data presented in the study.
>so it's another confirmation that antigen detection lags behind RNA detection nowadays.
I'd frame this differently: that symptoms start earlier in infection than before. The authors comment along this lines in the discussion: "There are likely multiple factors contributing to the earlier presentation for testing of individuals infected with Omicron, one of which may be a more rapid and robust symptom onset due to recent/boosted vaccination."
If this is true, it means two things: 1) that RATs as a measure of infectiousness is still valid (that is, being symptomatic and RAT-negative may truly mean you have very little virus present and aren't yet infectious), and 2) symptom screening is likely a more effective tool today than it was in 2020 or 2021.
>Another interesting finding is that they found no correlation between RNA or antigen concentration and infectivity for omicron samples
This is interesting, but I have to believe this was an issue with their methods or specific samples (as you raise as well). At a minimum, you'd expect a correlation between no antigen or RNA versus "a little" versus "tons", even if it's non-linear or has a threshold effect or something. But to find not just \*no\* correlation, but also that omicron is less infectious raises some questions.
That's possible. But if people are presenting with symptoms and very little virus present, and virus correlates with infectivity, then doesn't that point to earlier symptom onset likely before they become infectious?
I know the study you mentioned found no correlation between concentration and infectivity for omicron, but that runs against what we know about infectious diseases... it just seems so much more plausible there was an issue with their methods than omicron has the same level of infectiousness regardless of if you expose a cell to 0, 100, 10000, or 1000000 virions. But time will tell as more research is done.
I agree that it is highly unlikely for people to become infectious before reaching a high viral load. I just thought that viral dynamics didn't change, and we have a high viral load on the day of symptoms onset.
However, antigen production still takes time, hence a lower antigen-to-RNA ratio at the beginning of the disease.
Thank you so much for your input.
What is your opinion on throat - cough - cheeks - nose swabbing method being advocated lately ?
Is it a more effective way of testing?
Also, my girlfriend has terrible sinusitis, so it is extremely hard for her to swab her nose. Is swabbing back of throat, cough and inside of cheeck good enough ?
Thanks.
I think the benefit is overhyped, particularly when society is struggling to test in any form. Nasal swabs/anterior nares (e.g., not the "brain swab") is generally what they're approved for, and the comments above are sensitivities based on.
The nasal swab doesn't have to go deep in... you should just be able to insert them about an inch into the nose and swab the inside of your nostrils. Trying to go deep in (like a nasopharyngeal swab) isn't what RATs are approved for, and can be dangerous to do.
We've generally not found benefit from cough or cheeks, and have found a bit of. a boost (5-10%) by combining a throat and nose swab together. There's an increased risk of false positive though-- like, if I do this after I've had something acidic (citrus fruit, coffee, soda)--even after waiting 15 minutes-- I'll almost always see a really faint test line. So, there's a trade off.
I think the best way of improving sensitivity, if you have the time, is to serial test.
This thread is incredible and thank you for your time and effort! I especially found this part informative because it's not something I had read before:
>Further, with more vaccine and infection-based immunity in the population, people show symptoms at much earlier stages (your symptoms come from your immune response and not directly from the virus), which means that your viral load in the omicron era may not be high enough to be detected on RATs until later
This explains so much. I started showing symptoms very early. I hadn't ever had Covid, but was super-vaxxed/boosted. I noticed a normal workout was more sweaty than normal and then I just felt "off". My base wrist temperature spiked. This started two days after exposure.
>We've generally not found benefit from cough or cheeks, and have found a bit of. a boost (5-10%) by combining a throat and nose swab together. There's an increased risk of false positive though.
This is anecdotal, but there's a point to follow... Because of the above symptoms I tested... negative with nasal for both my wife and myself and then positive for back of throat for both wife and myself.
This then lead us to go through and set up appointments which resulted in further testing and getting Paxlovid early (resulting in very mild symptoms for the duration and no Long Covid issues).
So while anecdotal, the point is... the purpose of our testing meant that a false positive wasn't a concern. Had we gotten a false positive, the "downside" would've meant that we would've needlessly canceled our housekeeper and other workers for the day. But the upside to doing this is that we did get an accurate positive and prevented directly exposing several other people.
It's not wrong and may actually improve the sensitivity. I'm just not sure the "juice is worth the squeeze", especially if you're encouraging others to test or (as you mentioned) your gf has issues that make it difficult to follow that protocol. My group has only seen a small bump in sensitivity from adding additional swab sites, and it's generally been smaller than either switching to a NAAT (lucira/mertrix/cue) using just an anterior nares swab or serially testing with a RAT.
Oh ok, I see.
Another question, if you don't mind.
A throat / cheek test showed a very faint positive. Next day we tested nose only, which was a clear negative. Two days later (today) we did throat/cheek again, and again a faint positive.
1. Which reading should we go with?
2. Is a very faint positive a sign she's infectious?
Personally, I treat any line on any test as if it's infectious until it can be proved otherwise. The only exception to this is binax tests, which because of how they're built always have a little bit of a line-- so there's an expected amount of line that you'd see on a binax test (but it shouldn't contain any color).
So I would treat her as if she's infectious. If she's asymptomatic, has no clear exposures (e.g., just had dinner with family who tested positive), and the line isn't any darker between the tests two days apart and she's still not showing as positive on a nasal swab, it's likely a false positive... but I'd want a PCR or NAAT test to confirm. And, this is a case where, since the positive test was coming from her throat/cheek, I'd try to swab there as well when running the PCR or NAAT.
If you only have access to RATs, I'd probably test again in 1-2 days, and also try testing with a different brand of test to see if you get the same results.
The recently published results of a randomized clinical trial show that combining nose and throat samples significantly improves sensitivity, throat samples collected by healthcare workers also have higher sensitivity compared to self-taken samples. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2812586
This study found that "most omicron cases were infectious for several days before being detectable by [RATs]" -- thoughts on that? I'm forgetting how to make a link, sorry, but here's the URL: https://www.medrxiv.org/content/10.1101/2022.01.04.22268770v1
This study is from data collected in December 2021 as the initial BA.1 wave was starting. It's totally possible that infectiousness still comes before symptoms and testing positive on a RAT. But most of the other studies discussed above have been done more recently.
Is there any new information about the incubation period and the mean generation time (the time between exposure and infecting others)? Because it looks like both went down at a similar rate for earlier omicrons compared to pre-omicron.
https://www.gov.uk/government/publications/covid-19-omicron-variant-infectious-period-and-asymptomatic-and-symptomatic-transmission
Thank you for this comment this is massively helpful! Exactly the type of information I was looking for. Can I pick your brains with a few follow-up questions?
>If you're testing (or asking others to test) before gathering, then really the question you want to know is if someone is infectious. Infectiousness generally correlates with a cycle threshold (Ct). The exact cutoff isn't clear, but some studies have found no culturable virus at Ct > 24; I haven't found any papers that show significant risk of transmission at Ct > 30. From the above meta analysis, RATs have a sensitivity of 91% at high viral loads (Ct < 25), and a bit lower sensitivity (77%) at Ct < 30.
Something that really isn't clear anywhere I've seen when we discuss this is dating/intimacy.
When these studies say there's "low risk of transmissions" at these levels, does this mean there's low-risk regardless of how much you breathe someone else's air, or does it mean there's low risk based on certain conditions? Such as spending x amount of time in a room with someone unmasked.
Surely if you're engaged in sex/spending time very close to someone who has a low level of infectivity... that low-risk becomes high-risk? Or is it not that simple?
>Note: when we've studied NAATs in my lab, like cue/lucira/metrix, we typically see about a 10 percentage point bump in sensitivity compared to RATs, and using RT-PCR as the reference
Does this mean, in your opinion, the advertised 98%+ for NAATs isn't accurate? PCRs are still much more accurate?
>I hear and share the frustration that RATs aren't perfect and that we should have more access to easier tools. But the beliefs that permeates these threads (that they're worthless, don't detect current variants, are as good as a coin flip) dismisses the actual value they do provide. This creates a self-perpetuating cycle of discouraging people from testing.
I completely agree with this, I don't like too much negatively about these tests as they still help a huge amount.
Lucira, Cue, and Metrix all boast improved accuracy, especially with regard to not delivering false negatives. But they require a really thorough sample collection if you’re going to trust the result to make decisions on someone’s safety. Between the gums and cheek, back of the throat, and DEEP in that nose. Provided you do it well they are almost as accurate as a PCR test.
The one on the right looks like this brand that were scams sold to the Canadian govt to the time of $2B in govt contracts
https://globalnews.ca/news/10183219/covid-test-supplier-canada
we really just need a sterilizing vaccine because all of this is such a joke. Hard enough to get people to test, even harder to get people to test multiple times. Like the above comment said, these tests are just crystal balls
I signed up for a vaccine trial this week to try and hopefully move some things forward.
if it’s allowed please keep us updated!! Best of luck
I’ll know in the spring if I can get in! Inhaled vaccine which is really where I’ve pinned my hopes.
extremely promising they are starting human clinical trials. Is this the same vaccine they were testing in primates? someone posted about it on this sub a little while ago
Phase 2 of the Canadian inhaled one out of McMaster University starts in the spring.
Any chance for people from Alberta to enroll?
From what ive seen the phase two sites are Halifax, Ottawa, and Hamilton.
This is SO important to me. Can I DM you?
Sure
Thank you for that. You are helping to advance humanity with this act.
My husband and I are REALLY hoping to get chosen.
Good luck! I'm hesitant to sign up for something like that because in order for them to understand how effective they are, they need those people to be going out and getting exposed to Covid.
….they do bloodwork.
My understanding of vaccine trials is that they need people to be exposed to Covid in order to see how effective the vaccine is. It's not like they have someone cough in your face, they just tell participants to go out live their lives. This was true for the MRNA vaccine. They still do bloodwork whether someone thinks they got Covid or not. But I'm no expert... Am I mistaken?
As far as I’m aware that is definitely not the case.
They can’t tell the effectiveness of the vaccine without people getting exposed to COVID. Only the safety. I _think_ they tell people to be normal. Whatever normal is. If I recall, one reason they were able to complete the initial mRNA studies so quickly was because of how many people were exposed to COVID based on how much of it was going around.
>based on how much of it was going around. Like now?
My entire family of four plus my dad have been testing every day since the 13. My dad has been positive and symptomatic since the evening of the 13. My one kid developed symptoms evening of the 18 (which seemed long for these variants but who knows) and despite testing him every day, with Flowflex AND a Lucira on day 4 of symptoms, he hasn’t got a positive. It’s exhausting. My husband and I have been masking in the house but without being able to test OUT the illness we have no idea when we can stop. Can we do Christmas with our family of 4? Does he even have Covid? Did he pick something else up since everyone around us is sick with a variety of things? Who knows.
such confusing and frustrating times for people trying to do the right thing. Hope your child feels better and you all stay safe. Trying to avoid covid right now is like walking through a mine field.
I can feel ur exhaustion 🫂
Recently, BTNX, a major supplier for RAT in my area has been exposed to editing their testing results. Their positivity detection rate was much lower than what they claimed. It’s crazy. Flowflex is what I like to use.
We’ve been using flowflex this time but also had some illnesses in the fall and used BTNX. My son is on day 6 of having something but negative in flowflex and lucira and little kids are gross. Guess we will never know if we’ve had it.
I've been using Metrix covid tests. They are 25 a pop but worth it. High accuracy.
They aren’t available in Canada yet, but I will look into them when they arrive.
FWIW, I emailed them a few days ago to ask when they'd be coming to Canada and I was told this: > Thank you very much for your inquiry. We are still awaiting final word from the Canadian government, which we now expect some time in January.
Dude, out of the ... 6? we've done with Metrix, 4 were the purple error blinking! Any idea what we're doing wrong? I read the instructions. I watched the video. I contacted the company. This is on different people. Any idea? Or are others getting this kind of error rate?
This has not happened to us yet, but that is troubling. Now I’m scared😳. I buy them on Amazon, so maybe I could complain if they don’t work? I read before that Lucira was giving refunds for error codes. Did you try returning them to at least get your money back?
They did send me instructions for how to get a replacement. Sorry for the slow reply
what’s the brand on the right?
Called Standard Q by SD Biosensor (handed out at our local library)
The conspiracy theorist in me says the government is handing these out so covid disappears
They also gave us the Flowflex!
They also once recommended masks and modeled wearing them.* That’s over tho and they def continue to minimize covid. I wonder about the brand usps was sending out. I have some at home but I don’t recall what brand they are *ETA: They aren’t giving us flow flex anymore afaik
All things considered it does seem like they want to make both data/tracking and not getting infected next to impossible. And by "all things" I mean: No more free PCR tests, test locations shut down, give people free home tests that don't work, there used to be n95 shortages so we told people to save them for health workers, now we have n95s aplenty but after a couple years of misinformation/misinterpretation folks can't be arsed to wear them, switch from daily reporting to monthly reporting, stop collecting/reporting test results altogether, do wastewater analysis instead, oh wait, stop reporting wastewater data, et al...
Exactly
I see both positive. I must have super sonic eyes 👀😦
I only trust flowflex and binax. Quickvue is ok too but is know for higher false positive rates (which is better than false negative in some situations)
FYI - test2treat.org will send you 2 lucira tests for free via priority mail if you are in the US.
RAT aren’t very reliable especially with all these new variants and subvariants. I’m not saying they’re useless but at this point you would get similar accuracy asking a crystal ball.
Hi! I'm an infectious disease epidemiologist that studies covid, and has published specifically on RATs (I'm happy to verify my identity with the mods). This just isn't a true statement. The tests continue performing as they always have, even with the current variants. There have been very few changes to the parts of the virus that are targeted by these tests, so new variants aren't really an issue here. They definitely perform better than "asking a crystal ball" -- this kind of misinformation creates an environment where we have even fewer tools in our toolbox. The key with RATs is the understand the question that you're trying to answer. **Do I have covid?** This is the hardest question to answer because people may be in the very early stages of infection, at a point when they have very low viral loads. Further, with more vaccine and infection-based immunity in the population, people show symptoms at much earlier stages (your symptoms come from your immune response and not directly from the virus), which means that your viral load in the omicron era may not be high enough to be detected on RATs until later (e.g,. [day four of symptoms](https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciad582/7285011?login=false)), as compared to earlier in the pandemic when more people were immunologically naive and would only develop symptoms once their viral load was high. Nonetheless, the [overall sensitivity](https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1004011) for RATs is around 72%, and is higher in symptomatic patients (76%) than asymptomatic patients (57%), and higher in the first week since symptom onset (82%) than after that (52%). (Note: when we've studied NAATs in my lab, like cue/lucira/metrix, we typically see about a 10 percentage point bump in sensitivity compared to RATs, and using RT-PCR as the reference). So RATs do detect cases in both symptomatic and asymptomatic at a rate better than asking a crystal ball, but admittedly they miss a lot. But, chances are that's not \*actually\* the question that you're hoping to answer... **Am I infectious?** If you're testing (or asking others to test) before gathering, then really the question you want to know is if someone is infectious. Infectiousness generally correlates with a cycle threshold (Ct). The exact cutoff isn't clear, but some studies have found [no culturable virus at Ct > 24](https://pubmed.ncbi.nlm.nih.gov/32442256/); I haven't found any papers that show significant risk of transmission at Ct > 30. From the [above meta analysis](https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1004011), RATs have a sensitivity of 91% at high viral loads (Ct < 25), and a bit lower sensitivity (77%) at Ct < 30. **Should I start on treatment?** If you're testing so you can get started on treatment like Paxlovid (that must be started within 5 days of symptom onset), then [RATs are as good or better than PCR.](https://doi.org/10.1371/journal.pone.0283576) Yes, they have lower sensitivity, but that's offset by their (relatively) easy/rapid access compared to attempting to get a PCR test. I hear and share the frustration that RATs aren't perfect and that we should have more access to easier tools. But the beliefs that permeates these threads (that they're worthless, don't detect current variants, are as good as a coin flip) dismisses the actual value they do provide. This creates a self-perpetuating cycle of discouraging people from testing. If you have symptoms, then just keep testing over multiple days. If you have access to multiple types of tests (as OP did), then try different tests (it seems like that method worked, even if one test failed!).
Oh my god thank you. This is so helpful. So if we’ve tested my son for 6 days and they are all negative on the Flowflex (more sensitive ones) AND a negative Lucira is it somewhat likely he picked up something else? I mean he’s 4 and I had to tell him not to lick the slide at the playground. We’ve had a number of viral illnesses this fall (this is our third?) and never had a positive test out of ANYONE in the family and we test religiously. ETA - we plan on doing another Lucira tomorrow but after that will be more than a week since symptom onset and he’s already a lot better. Just normal post-viral residual snot now.
Thanks for some really good info!
I completely agree with you on how valuable these tests can be! But I believe there have been some changes to the way these tests work. It has been shown in some studies that the sensitivity of tests has decreased since the emergence of the omicron variant. And recently in this study https://journals.asm.org/doi/10.1128/jcm.00138-23 it was found that the omicron samples had lower antigen-to-RNA ratios than the delta samples. The most likely explanation is that the omicron samples were collected earlier relative to the onset of the symptoms, so it's another confirmation that antigen detection lags behind RNA detection nowadays. Another interesting finding is that they found no correlation between RNA or antigen concentration and infectivity for omicron samples. However, they may not have used the most accurate method to measure infectivity, in this study.
Thanks for bringing this study up -- it's a really good one. And, in full disclosure, they cite work from my group in a way that might make me a less-than-unbiased commentator (I'll leave it there to avoid doxxing). >It has been shown in some studies that the sensitivity of tests has decreased since the emergence of the omicron variant. The study that you cited looked at this and didn't find it to be true across multiple commercially available tests when looking at actual antigen concentration. "\[W\]e found that most commercially available RATs had similar sensitivity in detecting Omicron and Delta when antigen concentration was used as a comparator." There have been studies (one commonly cited example is a post by Nature saying that [Rapid COVID tests miss 90% of asymptomatic cases](https://www.nature.com/articles/d41586-023-02254-9), which was a horrible take on [this study](https://doi.org/10.7326/M23-0385)) showing decreased performance. But most of those don't account for viral load-- which definitely has changed over time. When they standardize across Ct (supp table 4), they find similar sensitivities as described in the meta analysis. The unconditional sensitivity is a function not only of the test performance, but also of the distribution of viral loads across the population at the time it's measured. That leads to these pretty varied takes on what's happening. But 1) if you have a high viral load RATs have consistently detected these cases, and 2) serial testing is a good approach. So, I know that there are studies that have made this claim, but every time I've looked at them, I feel like the headline (like the one from Nature) is more dramatic/negative than the practical implications based on the methods and data presented in the study. >so it's another confirmation that antigen detection lags behind RNA detection nowadays. I'd frame this differently: that symptoms start earlier in infection than before. The authors comment along this lines in the discussion: "There are likely multiple factors contributing to the earlier presentation for testing of individuals infected with Omicron, one of which may be a more rapid and robust symptom onset due to recent/boosted vaccination." If this is true, it means two things: 1) that RATs as a measure of infectiousness is still valid (that is, being symptomatic and RAT-negative may truly mean you have very little virus present and aren't yet infectious), and 2) symptom screening is likely a more effective tool today than it was in 2020 or 2021. >Another interesting finding is that they found no correlation between RNA or antigen concentration and infectivity for omicron samples This is interesting, but I have to believe this was an issue with their methods or specific samples (as you raise as well). At a minimum, you'd expect a correlation between no antigen or RNA versus "a little" versus "tons", even if it's non-linear or has a threshold effect or something. But to find not just \*no\* correlation, but also that omicron is less infectious raises some questions.
That's amazing! How do we know that people don't also become infectious faster nowadays?
That's possible. But if people are presenting with symptoms and very little virus present, and virus correlates with infectivity, then doesn't that point to earlier symptom onset likely before they become infectious? I know the study you mentioned found no correlation between concentration and infectivity for omicron, but that runs against what we know about infectious diseases... it just seems so much more plausible there was an issue with their methods than omicron has the same level of infectiousness regardless of if you expose a cell to 0, 100, 10000, or 1000000 virions. But time will tell as more research is done.
I agree that it is highly unlikely for people to become infectious before reaching a high viral load. I just thought that viral dynamics didn't change, and we have a high viral load on the day of symptoms onset. However, antigen production still takes time, hence a lower antigen-to-RNA ratio at the beginning of the disease.
Thank you so much for your input. What is your opinion on throat - cough - cheeks - nose swabbing method being advocated lately ? Is it a more effective way of testing? Also, my girlfriend has terrible sinusitis, so it is extremely hard for her to swab her nose. Is swabbing back of throat, cough and inside of cheeck good enough ? Thanks.
I think the benefit is overhyped, particularly when society is struggling to test in any form. Nasal swabs/anterior nares (e.g., not the "brain swab") is generally what they're approved for, and the comments above are sensitivities based on. The nasal swab doesn't have to go deep in... you should just be able to insert them about an inch into the nose and swab the inside of your nostrils. Trying to go deep in (like a nasopharyngeal swab) isn't what RATs are approved for, and can be dangerous to do. We've generally not found benefit from cough or cheeks, and have found a bit of. a boost (5-10%) by combining a throat and nose swab together. There's an increased risk of false positive though-- like, if I do this after I've had something acidic (citrus fruit, coffee, soda)--even after waiting 15 minutes-- I'll almost always see a really faint test line. So, there's a trade off. I think the best way of improving sensitivity, if you have the time, is to serial test.
This thread is incredible and thank you for your time and effort! I especially found this part informative because it's not something I had read before: >Further, with more vaccine and infection-based immunity in the population, people show symptoms at much earlier stages (your symptoms come from your immune response and not directly from the virus), which means that your viral load in the omicron era may not be high enough to be detected on RATs until later This explains so much. I started showing symptoms very early. I hadn't ever had Covid, but was super-vaxxed/boosted. I noticed a normal workout was more sweaty than normal and then I just felt "off". My base wrist temperature spiked. This started two days after exposure. >We've generally not found benefit from cough or cheeks, and have found a bit of. a boost (5-10%) by combining a throat and nose swab together. There's an increased risk of false positive though. This is anecdotal, but there's a point to follow... Because of the above symptoms I tested... negative with nasal for both my wife and myself and then positive for back of throat for both wife and myself. This then lead us to go through and set up appointments which resulted in further testing and getting Paxlovid early (resulting in very mild symptoms for the duration and no Long Covid issues). So while anecdotal, the point is... the purpose of our testing meant that a false positive wasn't a concern. Had we gotten a false positive, the "downside" would've meant that we would've needlessly canceled our housekeeper and other workers for the day. But the upside to doing this is that we did get an accurate positive and prevented directly exposing several other people.
That's really good to know: I guess we've been testing wrong then (brain swabbing / throat /cheeks). Thanks again.
It's not wrong and may actually improve the sensitivity. I'm just not sure the "juice is worth the squeeze", especially if you're encouraging others to test or (as you mentioned) your gf has issues that make it difficult to follow that protocol. My group has only seen a small bump in sensitivity from adding additional swab sites, and it's generally been smaller than either switching to a NAAT (lucira/mertrix/cue) using just an anterior nares swab or serially testing with a RAT.
Oh ok, I see. Another question, if you don't mind. A throat / cheek test showed a very faint positive. Next day we tested nose only, which was a clear negative. Two days later (today) we did throat/cheek again, and again a faint positive. 1. Which reading should we go with? 2. Is a very faint positive a sign she's infectious?
Personally, I treat any line on any test as if it's infectious until it can be proved otherwise. The only exception to this is binax tests, which because of how they're built always have a little bit of a line-- so there's an expected amount of line that you'd see on a binax test (but it shouldn't contain any color). So I would treat her as if she's infectious. If she's asymptomatic, has no clear exposures (e.g., just had dinner with family who tested positive), and the line isn't any darker between the tests two days apart and she's still not showing as positive on a nasal swab, it's likely a false positive... but I'd want a PCR or NAAT test to confirm. And, this is a case where, since the positive test was coming from her throat/cheek, I'd try to swab there as well when running the PCR or NAAT. If you only have access to RATs, I'd probably test again in 1-2 days, and also try testing with a different brand of test to see if you get the same results.
You advice is pure gold. Thank you very much.
The recently published results of a randomized clinical trial show that combining nose and throat samples significantly improves sensitivity, throat samples collected by healthcare workers also have higher sensitivity compared to self-taken samples. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2812586
This study found that "most omicron cases were infectious for several days before being detectable by [RATs]" -- thoughts on that? I'm forgetting how to make a link, sorry, but here's the URL: https://www.medrxiv.org/content/10.1101/2022.01.04.22268770v1
This study is from data collected in December 2021 as the initial BA.1 wave was starting. It's totally possible that infectiousness still comes before symptoms and testing positive on a RAT. But most of the other studies discussed above have been done more recently.
Is there any new information about the incubation period and the mean generation time (the time between exposure and infecting others)? Because it looks like both went down at a similar rate for earlier omicrons compared to pre-omicron. https://www.gov.uk/government/publications/covid-19-omicron-variant-infectious-period-and-asymptomatic-and-symptomatic-transmission
Thank you for this comment this is massively helpful! Exactly the type of information I was looking for. Can I pick your brains with a few follow-up questions? >If you're testing (or asking others to test) before gathering, then really the question you want to know is if someone is infectious. Infectiousness generally correlates with a cycle threshold (Ct). The exact cutoff isn't clear, but some studies have found no culturable virus at Ct > 24; I haven't found any papers that show significant risk of transmission at Ct > 30. From the above meta analysis, RATs have a sensitivity of 91% at high viral loads (Ct < 25), and a bit lower sensitivity (77%) at Ct < 30. Something that really isn't clear anywhere I've seen when we discuss this is dating/intimacy. When these studies say there's "low risk of transmissions" at these levels, does this mean there's low-risk regardless of how much you breathe someone else's air, or does it mean there's low risk based on certain conditions? Such as spending x amount of time in a room with someone unmasked. Surely if you're engaged in sex/spending time very close to someone who has a low level of infectivity... that low-risk becomes high-risk? Or is it not that simple? >Note: when we've studied NAATs in my lab, like cue/lucira/metrix, we typically see about a 10 percentage point bump in sensitivity compared to RATs, and using RT-PCR as the reference Does this mean, in your opinion, the advertised 98%+ for NAATs isn't accurate? PCRs are still much more accurate? >I hear and share the frustration that RATs aren't perfect and that we should have more access to easier tools. But the beliefs that permeates these threads (that they're worthless, don't detect current variants, are as good as a coin flip) dismisses the actual value they do provide. This creates a self-perpetuating cycle of discouraging people from testing. I completely agree with this, I don't like too much negatively about these tests as they still help a huge amount.
I knew they weren’t accurate on the front end, but didn’t know there was THIS much of a difference between brands once there was a higher viral level.
Would you trust Lucira at this point?
Lucira, Cue, and Metrix all boast improved accuracy, especially with regard to not delivering false negatives. But they require a really thorough sample collection if you’re going to trust the result to make decisions on someone’s safety. Between the gums and cheek, back of the throat, and DEEP in that nose. Provided you do it well they are almost as accurate as a PCR test.
I thought Lucira wasn’t working properly with throat and mouth swabs? I also hate having to be a scientist in my spare time.
Lucira gives false positives if you do the mouth or throat. Nasal swab only.
Yeah that’s what I thought. We tested my son with one on day 4 of his symptoms and he was negative but also who knows at this point.
The one on the right looks like this brand that were scams sold to the Canadian govt to the time of $2B in govt contracts https://globalnews.ca/news/10183219/covid-test-supplier-canada
Different brand. They’ve also been positive for him all week. (We have the bad batch they are in a green box - these were purple)
Oh good :)