3 ms·

> Further, any variance of susceptibility or contact density means you don't need to reach 60% for herd immunity. Some estimates say that the real threshold may

> Further, any variance of susceptibility or contact density means you don't need to reach 60% for herd immunity. Some estimates say that the real threshold may likely be 25% or less: e.g. https://www.medrxiv.org/content/10.1101/2020.04.27.20081893v.. https://www.medrxiv.org/content/10.1101/2020.04.27.20081893v.... Further, lighter weight social distancing measures can further reduce Rt and attain herd immunity at a lower percentage. Not surprisingly, that paper has had some discussion: https://twitter.com/CT_Bergstrom/status/1257452758376091648 https://twitter.com/CT_Bergstrom/status/1257452758376091648 > It is true that if you could somehow pick and choose who became immune — the way you can in principle with vaccination — you might be able to do pretty well, vaccinating the high-contact individuals only and reaching herd immunity at low levels of vaccination. > But natural infections don't spread like this. High-contact individuals are connected to low contact individuals. An epidemic spreads organically through the population, infecting who it happens to, not who you want it to. > IF high contact individuals were only connected to other high contact individuals with high probability, you still might make some headway with nature disease progression. This sort of thing can matter for STD transmission. > Respiratory viruses tend to be different. You have household transmission, cohort-based (school/work) transmission, and incidental transmission (subway/supermarket). These render the transmission network quite well-connected. Additionally, if we're talking natural infection to get to herd immunity, you have the issue of overshoot, so unless you're very precise on measures to tamp down on transmission before you get to herd immunity levels, you easily overshoot the herd immunity threshold by quite a bit.

mlyle 6y ago
> > But natural infections don't spread like this. High-contact individuals are connected to low contact individuals. An epidemic spreads organically through the population, infecting who it happens to, not who you want it to. Surely high contact people are infected -more-, though, no? In many ways, R0 is a "somewhat worst case number", in that it's something you observe in a population where the virus propagates well. There are likely to be other populations that it doesn't spread quite so well in-- either because of innate susceptibility or behavior differences. > Additionally, if we're talking natural infection to get to herd immunity, you have the issue of overshoot, so unless you're very precise on measures to tamp down on transmission before you get to herd immunity levels, you easily overshoot the herd immunity threshold by quite a bit. Exponential processes with a lot of delay and noise are a difficult controls problem, but it wouldn't be hard for jurisdictions that are doing well to target Rt=~ 0.95 .. 1.1 with interventions instead of trying to maintain Rt =~ 0.8. Of course, you need to be prepared to react quickly if things look like they are getting out of hand. And, thankfully, as the susceptible population drops the control problem gets a lot easier, because there's a ceiling of how high Rt can get...

mlyle 6y ago

> > But natural infections don't spread like this. High-contact individuals are connected to low contact individuals. An epidemic spreads organically through the population, infecting who it happens to, not who you want it to. Surely high contact people are infected -more-, though, no? In many ways, R0 is a "somewhat worst case number", in that it's something you observe in a population where the virus propagates well. There are likely to be other populations that it doesn't spread quite so well in-- either because of innate susceptibility or behavior differences. > Additionally, if we're talking natural infection to get to herd immunity, you have the issue of overshoot, so unless you're very precise on measures to tamp down on transmission before you get to herd immunity levels, you easily overshoot the herd immunity threshold by quite a bit. Exponential processes with a lot of delay and noise are a difficult controls problem, but it wouldn't be hard for jurisdictions that are doing well to target Rt=~ 0.95 .. 1.1 with interventions instead of trying to maintain Rt =~ 0.8. Of course, you need to be prepared to react quickly if things look like they are getting out of hand. And, thankfully, as the susceptible population drops the control problem gets a lot easier, because there's a ceiling of how high Rt can get...