Yeah the “ethical rules” linked tweet asks, since tests are available in the UK, what if we just had Londoners take two—one in the nose and one in the throat, to see if they work? (so a non-confident version of #3) It’s more complicated too, not just #2 of developing tests we know work with saliva. From the linked preprint, the viral loads are somewhat higher in saliva than nasal earlier but nasal than saliva later (low sample size for this inference though).
And those data are a bit sad as they show that regardless of the saliva/nasal viral loads, antigen struggles even for high viral loads until day 3 post-PCR-positive. PCR can detect pre-symptomatic cases (so day 0 PCR-positive can be...fudging a bit for the shorter serial interval, maybe day −3 of symptoms for omicron), which implies that taking an antigen test when you develop symptoms is right on day 3 post-PCR-positive. Maybe the FDA was getting signals of this (additional citations also included in the linked preprint) when they issued their cryptic statement about lower antigen sensitivity for omicron. It feels like we had more wiggle room on an informative antigen testing window for delta than we do for omicron. Antigen testing was weakly informative pre-symptoms for delta, but, based on this preprint, it seems antigen testing is wholly uninformative pre-symptoms for omicron.
A single omicron antigen test is good after showing symptoms, not before (Table 1). The good news is antigen doesn’t miss randomly (of course not) - it misses lower viral load cases (Figure 1a). But we can’t be sure those cases are at a steady-state of viral load, so it doesn’t necessarily ensure that missed cases remain low viral load. Asymptomatic cases tend to be lower viral load than symptomatic cases (makes sense), but it’s by no means a guarantee (Figure 1b-c, median Ct of symptomatic is ~25 while median Ct of asymptomatic is ~30, higher Ct means lower viral load). https://www.medrxiv.org/content/10.1101/2022.01.08.22268954v2.full.pdf+html
Yeah the “ethical rules” linked tweet asks, since tests are available in the UK, what if we just had Londoners take two—one in the nose and one in the throat, to see if they work? (so a non-confident version of #3)
It’s more complicated too, not just #2 of developing tests we know work with saliva. From the linked preprint, the viral loads are somewhat higher in saliva than nasal earlier but nasal than saliva later (low sample size for this inference though).
And those data are a bit sad as they show that regardless of the saliva/nasal viral loads, antigen struggles even for high viral loads until day 3 post-PCR-positive. PCR can detect pre-symptomatic cases (so day 0 PCR-positive can be...fudging a bit for the shorter serial interval, maybe day −3 of symptoms for omicron), which implies that taking an antigen test when you develop symptoms is right on day 3 post-PCR-positive. Maybe the FDA was getting signals of this (additional citations also included in the linked preprint) when they issued their cryptic statement about lower antigen sensitivity for omicron. It feels like we had more wiggle room on an informative antigen testing window for delta than we do for omicron. Antigen testing was weakly informative pre-symptoms for delta, but, based on this preprint, it seems antigen testing is wholly uninformative pre-symptoms for omicron.
A single omicron antigen test is good after showing symptoms, not before (Table 1). The good news is antigen doesn’t miss randomly (of course not) - it misses lower viral load cases (Figure 1a). But we can’t be sure those cases are at a steady-state of viral load, so it doesn’t necessarily ensure that missed cases remain low viral load. Asymptomatic cases tend to be lower viral load than symptomatic cases (makes sense), but it’s by no means a guarantee (Figure 1b-c, median Ct of symptomatic is ~25 while median Ct of asymptomatic is ~30, higher Ct means lower viral load).
https://www.medrxiv.org/content/10.1101/2022.01.08.22268954v2.full.pdf+html
Is it accurate to say that Ct count is similar to the # of zero bits of the density of RNA in the sample (expressed in binary)?