5 ms·

> The steady state is exactly 1, which is like balancing a pencil on its point. At exactly one, it's indeterminate; you could see a subexponential growth or de

> The steady state is exactly 1, which is like balancing a pencil on its point. At exactly one, it's indeterminate; you could see a subexponential growth or decay. With no exponential terms remaining, lower-order terms that are ordinarily hidden by exponential growth become the dominant observables. (Since epidemic spread is also random, you're much more likely to see the stochastic terms show up in the overall statistics in these cases. You really can be lucky or unlucky with Rt ~= 1, but there's no persistent luck with Rt >> 1.) This is also important before community spreading sets in, and it is the mechanism by which contact tracing can work. Rather than change the general susceptibility of the population to the disease (changing the effective reproduction number), contact tracing tries to operate at the level of individual cases in ways that cannot be scaled to uncontrolled community spreading (even if Rt is close to 1). > and the border closures kept mutations from traveling: and influenza is notoriously mutation-prone. Perhaps, but are influenza mutations an important effect within a single flu season? I know the determination of to-be-dominant strains has a great effect on the composition of each season's flu vaccine, but as far as I am aware we don't see declining flu vaccine efficacy over a season.

Pyramus 5y ago
By the way, now that we are already talking about R ~= 1 ... Over pretty much the last year you could observe, in different countries all around the world, that the reproduction number was 'magically' floating around 1. Only recently did I learn that this effect was puzzling for epidemiologists as well and was only solved around 2012 (?) in a model that assumes a network of information about the disease in parallel to the network of disease transmission. The resulting feedback loops lead to the meta-stability of R=1. Super interesting how society acts as this distributed information processor, similar to 'the market' in economics.
- marvin 5y ago
  A well-known Norwegian economic commentator pointed this out in a newspaper article a few weeks ago. You'll eventually be forced to maintain an R~=1 no matter what you do, so it's best for everyone if your cases have a low baseline when that happens. The measures will be the same, but the baseline risk can either be terrible or okay. You can almost see the phenomenon in real time during this pandemic. Countries that have low trust in authorities will still freak out when the epidemic hits biblical proportions, and do various forms of impromptu distancing measures which will bring the R number down. Then when the signs of panic subside, they'll loosen them. And so on. Societies with high trust in authorities will still pressure their authorities to loosen up when things feel safe, with predictible results, leading to further lockdowns.
  - LeCow 5y ago
    The economic deviation caused by governments over reacting is your biggest pressure. Unless you shut down all travel, bars, restaurants, schools, universities and dating. Then all of this will come back in the future and kick you in the teeth. Either we're going to have to accept this as a way of life, which is more detrimental. Or we're pushing off the inevitable.
    - marvin 5y ago
      No one has overreacted, unless you accept an outcome that both leads to improvised individual social distancing and the even worse worse economic devastation that follows. This was uncertain to most people last year, but now we’ve seen so many examples that it really shouldn’t be so controversial any longer. But if it wasn’t, we wouldn’t be discussing it. The covid virus is evolved to fit exactly into the niche of societal behavior where it will be a big fucking problem but not so bad that it’s immediately obvious to enough people.
samatman 5y ago
We're not talking about a single flu season, effectively we're talking about skipping an entire flu season. Influenza is pretty promiscuous. In normal conditions, very few people aren't exposed to it: either their existing immune resistance (vaccinated or otherwise) is up to the job, or it isn't. Mutation is therefore the primary driver of flu, year upon year. This is why vaccines are continually reformulated for a best-guess at what strains are going to be dominant. We had just concluded a northern-hemisphere flu season when travel restrictions started to kick in. This was followed by at least a 90% reduction in international travel, and for most of what remained, it was mandated that new arrivals isolate for long enough to eliminate any influenza they might have carried. Lockdowns would mean less mutation to begin with, since it happens in human hosts. And such mutations as did present are going to have a tough time jumping oceans, and even when they do arrive, spreading through the populace is substantially inhibited. Ironically, the universal mask mandates are likely to be more effective against flu than against COVID. Like it or not, masking has minimal effect on spreading aerosols, although using a "real" mask, and being pretty careful to wear it right, can mitigate inhaling those aerosols. Influenza is believed to be spreadable through aerosols, but the primary vector is droplets, while the opposite appears to be true for SARS2. Bog-standard cloth masks are fairly good at keeping droplets off people and surfaces.
- michaelmrose 5y ago
  People don't inhale 1 or 0 covid particles they inhale n particles where reducing the value of n makes transmission less likely. Keeping more of your spit to yourself reduces chance of transmission even if masks are imperfect.
- seoaeu 5y ago
  > Like it or not, masking has minimal effect on spreading aerosols [citation needed]
- MereInterest 5y ago
  > The overwhelming majority of transmission of SARS-CoV-2 is via large respiratory droplets as conclusively demonstrated by contact tracing studies, cluster investigations, the lack of infection spread in hospital settings with universal masking protocols and the low estimated R. https://www.pennmedicine.org/updates/blogs/penn-physician-blog/2020/august/airborne-droplet-debate-article https://www.pennmedicine.org/updates/blogs/penn-physician-bl... > The principal mode by which people are infected with SARS-CoV-2 (the virus that causes COVID-19) is through exposure to respiratory droplets carrying infectious virus. https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/scientific-brief-sars-cov-2.html https://www.cdc.gov/coronavirus/2019-ncov/science/science-br... From what I can tell, you may have your flu/covid mixed up. Covid is spread through respiratory droplets, the spread of which is reduced by wearing a mask.

Pyramus 5y ago

By the way, now that we are already talking about R ~= 1 ... Over pretty much the last year you could observe, in different countries all around the world, that the reproduction number was 'magically' floating around 1. Only recently did I learn that this effect was puzzling for epidemiologists as well and was only solved around 2012 (?) in a model that assumes a network of information about the disease in parallel to the network of disease transmission. The resulting feedback loops lead to the meta-stability of R=1. Super interesting how society acts as this distributed information processor, similar to 'the market' in economics.

marvin 5y ago
A well-known Norwegian economic commentator pointed this out in a newspaper article a few weeks ago. You'll eventually be forced to maintain an R~=1 no matter what you do, so it's best for everyone if your cases have a low baseline when that happens. The measures will be the same, but the baseline risk can either be terrible or okay. You can almost see the phenomenon in real time during this pandemic. Countries that have low trust in authorities will still freak out when the epidemic hits biblical proportions, and do various forms of impromptu distancing measures which will bring the R number down. Then when the signs of panic subside, they'll loosen them. And so on. Societies with high trust in authorities will still pressure their authorities to loosen up when things feel safe, with predictible results, leading to further lockdowns.
- LeCow 5y ago
  The economic deviation caused by governments over reacting is your biggest pressure. Unless you shut down all travel, bars, restaurants, schools, universities and dating. Then all of this will come back in the future and kick you in the teeth. Either we're going to have to accept this as a way of life, which is more detrimental. Or we're pushing off the inevitable.
  - marvin 5y ago
    No one has overreacted, unless you accept an outcome that both leads to improvised individual social distancing and the even worse worse economic devastation that follows. This was uncertain to most people last year, but now we’ve seen so many examples that it really shouldn’t be so controversial any longer. But if it wasn’t, we wouldn’t be discussing it. The covid virus is evolved to fit exactly into the niche of societal behavior where it will be a big fucking problem but not so bad that it’s immediately obvious to enough people.

samatman 5y ago

We're not talking about a single flu season, effectively we're talking about skipping an entire flu season. Influenza is pretty promiscuous. In normal conditions, very few people aren't exposed to it: either their existing immune resistance (vaccinated or otherwise) is up to the job, or it isn't. Mutation is therefore the primary driver of flu, year upon year. This is why vaccines are continually reformulated for a best-guess at what strains are going to be dominant. We had just concluded a northern-hemisphere flu season when travel restrictions started to kick in. This was followed by at least a 90% reduction in international travel, and for most of what remained, it was mandated that new arrivals isolate for long enough to eliminate any influenza they might have carried. Lockdowns would mean less mutation to begin with, since it happens in human hosts. And such mutations as did present are going to have a tough time jumping oceans, and even when they do arrive, spreading through the populace is substantially inhibited. Ironically, the universal mask mandates are likely to be more effective against flu than against COVID. Like it or not, masking has minimal effect on spreading aerosols, although using a "real" mask, and being pretty careful to wear it right, can mitigate inhaling those aerosols. Influenza is believed to be spreadable through aerosols, but the primary vector is droplets, while the opposite appears to be true for SARS2. Bog-standard cloth masks are fairly good at keeping droplets off people and surfaces.

michaelmrose 5y ago
People don't inhale 1 or 0 covid particles they inhale n particles where reducing the value of n makes transmission less likely. Keeping more of your spit to yourself reduces chance of transmission even if masks are imperfect.
seoaeu 5y ago
> Like it or not, masking has minimal effect on spreading aerosols [citation needed]
MereInterest 5y ago
> The overwhelming majority of transmission of SARS-CoV-2 is via large respiratory droplets as conclusively demonstrated by contact tracing studies, cluster investigations, the lack of infection spread in hospital settings with universal masking protocols and the low estimated R. https://www.pennmedicine.org/updates/blogs/penn-physician-blog/2020/august/airborne-droplet-debate-article https://www.pennmedicine.org/updates/blogs/penn-physician-bl... > The principal mode by which people are infected with SARS-CoV-2 (the virus that causes COVID-19) is through exposure to respiratory droplets carrying infectious virus. https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/scientific-brief-sars-cov-2.html https://www.cdc.gov/coronavirus/2019-ncov/science/science-br... From what I can tell, you may have your flu/covid mixed up. Covid is spread through respiratory droplets, the spread of which is reduced by wearing a mask.