Thanks for this post, it helped clarify some of my concerns about the upcoming holidays.
I’m surprised you don’t mention testing (PCR or antigen). What are your views on testing before an event? What would be a good protocol for testing before a specific event – test on the day of, a day before?
Regarding timing, I think you want to test the day of. The day before is probably fine too. But Delta seemed like it was progressing fast enough that a 1-day lag would lose you a large chunk of the effectiveness.
Regarding mentioning testing in general—I think it helps a little but not enough to matter in most cases. I’m under the impression that PCR tests have a false negative rate of about 50% and antigen tests 70%, which basically translates into risk of .5x and .7x for an event. But if you’re home for the holidays, you’d have to keep testing repeatedly if you wanted this risk multiplier to extend, otherwise you might just develop sickness later.
So a $30 test for people only matters if you are going to an event where the average person is losing more than an hour of life, which is maybe 1000+ microcovids. I don’t think this comes up super often. However, I guess it’s not crazy to take 7 tests over a week to save people several days of life over the holidays. Maybe I should have added this actually. I guess it just seems like it won’t be cost-effective for the overcautious people (and will be overused!) and won’t be attention-effective for the undercautious people. But probably I should have thought through and been clear about this.
I thought rapid tests were generally considered to have a much lower false negative rate for detecting contagiousness, though they often miss people who are infected but not yet contagious. I forget why I think this, and haven’t been following possible updates on this story, but is that different from your impression? (Here’s one place I think saying this, for instance: https://www.rapidtests.org/blog/antigen-tests-as-contagiousness-tests) On this story, rapid tests immediately before an event would reduce overall risk by a lot.
The main reason I don’t automatically make a huge adjustment for this is that it seemed that there were still ~25% false negatives at peak contagiousness by PCR according to some studies. And 40% false negatives a few days later. All sort of things are possible, like that these studies included many asymptomatic and acontagious cases, but having seen anecdotal corroboration of this phenomenon, I’m inclined to think something weird is going on.
But I should give some weight to it though—perhaps 2x less ineffective when compared to contagiousness, so maybe 60% efficacy for rapid and 75% for PCR?
Thank you! The general reasoning makes sense to me. This Cochrane review finds a false negative for asymptomatic individuals of 42% with antigen tests – which were not self-tests. Is your rate significantly higher because you’re thinking of self-administered antigen tests? In many European countries, you can get antigen self-tests for about $2-4 a piece, this might make a testing scheme more cost-effective.
Ah, stocking up on $2 tests would be awesome! That I would certainly endorse.
My reasoning on antigen false negatives is coming from a few lines of evidence. Perhaps I can share some later. But in short, 1) lots of studies have found much higher than average false negative rates, so results are high-variance/heterogeneous 2) my anecdotal counts of people around me concords with the above studies 3) my prior is fairly high on studies overestimating the efficacy of tests, based on BOTH lab conditions being extra controlled and on scientists being biased toward finding higher efficacy (and this affecting studies in a real way that is hard to control for). Thus my preferred resolution of the mystery between anecdotal efficacy and average study efficacy is that studies overestimate efficacy.
Thanks for this post, it helped clarify some of my concerns about the upcoming holidays.
I’m surprised you don’t mention testing (PCR or antigen).
What are your views on testing before an event?
What would be a good protocol for testing before a specific event – test on the day of, a day before?
Regarding timing, I think you want to test the day of. The day before is probably fine too. But Delta seemed like it was progressing fast enough that a 1-day lag would lose you a large chunk of the effectiveness.
Regarding mentioning testing in general—I think it helps a little but not enough to matter in most cases. I’m under the impression that PCR tests have a false negative rate of about 50% and antigen tests 70%, which basically translates into risk of .5x and .7x for an event. But if you’re home for the holidays, you’d have to keep testing repeatedly if you wanted this risk multiplier to extend, otherwise you might just develop sickness later.
So a $30 test for people only matters if you are going to an event where the average person is losing more than an hour of life, which is maybe 1000+ microcovids. I don’t think this comes up super often. However, I guess it’s not crazy to take 7 tests over a week to save people several days of life over the holidays. Maybe I should have added this actually. I guess it just seems like it won’t be cost-effective for the overcautious people (and will be overused!) and won’t be attention-effective for the undercautious people. But probably I should have thought through and been clear about this.
I thought rapid tests were generally considered to have a much lower false negative rate for detecting contagiousness, though they often miss people who are infected but not yet contagious. I forget why I think this, and haven’t been following possible updates on this story, but is that different from your impression? (Here’s one place I think saying this, for instance: https://www.rapidtests.org/blog/antigen-tests-as-contagiousness-tests) On this story, rapid tests immediately before an event would reduce overall risk by a lot.
Ah, good point.
The main reason I don’t automatically make a huge adjustment for this is that it seemed that there were still ~25% false negatives at peak contagiousness by PCR according to some studies. And 40% false negatives a few days later. All sort of things are possible, like that these studies included many asymptomatic and acontagious cases, but having seen anecdotal corroboration of this phenomenon, I’m inclined to think something weird is going on.
But I should give some weight to it though—perhaps 2x less ineffective when compared to contagiousness, so maybe 60% efficacy for rapid and 75% for PCR?
Thank you! The general reasoning makes sense to me.
This Cochrane review finds a false negative for asymptomatic individuals of 42% with antigen tests – which were not self-tests. Is your rate significantly higher because you’re thinking of self-administered antigen tests?
In many European countries, you can get antigen self-tests for about $2-4 a piece, this might make a testing scheme more cost-effective.
Ah, stocking up on $2 tests would be awesome! That I would certainly endorse.
My reasoning on antigen false negatives is coming from a few lines of evidence. Perhaps I can share some later. But in short, 1) lots of studies have found much higher than average false negative rates, so results are high-variance/heterogeneous 2) my anecdotal counts of people around me concords with the above studies 3) my prior is fairly high on studies overestimating the efficacy of tests, based on BOTH lab conditions being extra controlled and on scientists being biased toward finding higher efficacy (and this affecting studies in a real way that is hard to control for). Thus my preferred resolution of the mystery between anecdotal efficacy and average study efficacy is that studies overestimate efficacy.