Coronavirus news #6. As always, please point out my errors. Not an expert in this specific domain, but I have relevant training and am trying to keep up to date. I encourage those of you with relevant expertise to also spread your understanding as best you can.
1) It's happened without much fanfare, but it seems as though contact with surfaces is no longer thought to be a very important method of spreading the virus. In March, there was a lot of advocacy around using gloves, washing hands, & avoiding face touching. As more evidence has poured in, the cautions and analyses have shifted towards focussing strongly on inhalation of viruses. I have yet to see clear research on the relative risks (please tell me if you know!), but I think this is a fair summary of epidemiologists' present beliefs. I'm not saying that viruses do not spread through contact with surfaces, so continue to take reasonable precautions. But I offer this to allay the fears of friends who go to incredible lengths to sanitise everything they buy or that enters their house. Letting new acquisitions sit in the sun for a week is overkill.
2) Brazil and India have exponentially increasing case numbers despite lockdowns - in India's case, one of the most brutal in the world. The outbreaks are concentrated in some regions, so it is possible that they will get contained. But given exhaustion with the cruelly mismanaged lockdowns (at least in India), I'm doubtful they will be. And they have
20% of the world's population between them.
3) As a consequence, the situation right now is far worse than I think most people realise. Global daily deaths are slowly decreasing (currently ~3000 per day), driven by improvements in the situation in Europe and the US, which were hit worst. The news is moving on to the economy, tourism, protests, and so on as local situations seem to stabilise, and people get bored or desperate. But this apparent progress can be quickly reversed by just one or two new outbreaks that can happen anywhere, and these seed new outbreaks in turn. We do not have a single pandemic, but a patchwork. Regions/countries with outbreaks can be isolated, but the success rate needed to prevent them seeding new outbreaks is very high. Most countries have not displayed the competence needed. We are stuck in this situation till we have a vaccine.
4) As India's & Brazil's numbers rise, global daily deaths will start to increase again. We are now looking at possibly millions to even tens of millions of deaths. This probably seems unlikely to you and I hope it's totally wrong. But in March, the possibility of tens of thousands of deaths was seen by many as unwarranted pessimism, and hundreds of thousands as wild fantasy. And yet here we are. We ought to learn something from this about how unreliable gut impressions about worst-case scenarios and tail risks are. And perhaps eventually turn that insight towards another area where scientists have spent decades venting their spleens about tail risks: climate change.
5) A better argument for why millions of deaths is plausible: a few weeks ago, Spain and France did the biggest & best random testing programs run so far, helping to fill a massive gap in basic data. These found that the infection fatality rate is about 1%, just as epidemiologists have been saying since at least March. Remember that infection fatality rate is the % of people who ever got infected that die, which is the number we are most interested in. Most reports have been about the case fatality rate, which leaves out all the people who got infected but did not know about or report it; this varies a lot based on medical system and reporting practices. Also, about 5% of those countries had been infected (i.e. had antibodies) at the time. If the virus were to continue to spread, you would not get 20 times as many deaths, but you would get very large numbers that are in line with those that basic epidemiological models predicted months ago. Apply that logic and the basic numbers to other parts of the world and you gets millions to tens of millions.
6) A particularly worrisome pattern: there are many more young people infected and hospitalised in India and some other countries than was expected. There's multiple reasons why this may be, such as exposure patterns and data biases. There are more scary possibilities but right now no real evidence for them. But even so, outbreaks among young people are a massive threat to countries with much younger populations, where the hope was that the vulnerable elderly could be isolated while the young slowly return to work.
7) Since I'm thoroughly sick of the endless debate around Sweden and its tactics, allow me to point out stories from other countries that are not discussed much. Take Mongolia and Vietnam, which have had zero deaths between them with a combined population of 100 million. Zero. And they share a border with China! Senegal, though further away, has had about 40 deaths in a population of 31 million. Ghana: about 35 deaths among 16 million people. Ethiopia: 12 deaths out of 115 million. All these countries are relatively poor and lack the capacity of European and American healthcare systems, in terms of manpower, training, and technological sophistication. What they share is that they took action in January, while more developed countries did nothing. I'll add that they are also younger, but I think that is a less important factor. Ghana and Ethiopia are noteworthy, because I understand they implemented better contact tracing than most of Europe or the US. Ghana also tested large numbers of people by using pooled testing, an old method I discussed in the very first of these posts in March. Germany and India have also been using the same strategy, which should have been employed months ago. I was personally terrified about outbreaks in developing countries, and want to highlight that many of them have outperformed the wealthiest countries to an impressive degree, one that ought to shock us. They may yet suffer badly, but they have done well so far.
8) Reopening in many countries is politically inevitable now and justified in many cases. Did the lockdowns work? It's a question that's going to be contested very strongly because of the political and economic implications. But please keep in mind that this is not exactly a yes/no question. There was not a single type of 'lockdown'. Instead, there was a wide range of activity restrictions, ranging from stay-at-home with almost no exceptions (China, India, Italy, France) to limitations on gathering places such as restaurants & movie theatres but not much else (Switzerland) to essentially no legal limitations, just recommendations (Sweden, Ethiopia). There were successes in countries in all these categories. So a case could be made that the strictest stay-at-home orders were not needed, at least in areas without high population densities. But let's put that in context. Strict restrictions were entirely justifiable at the time given the limited information we had and the very real threat of having healthcare systems overwhelmed (as happened in northern Italy). Shutdowns were protection against very real tail risks. Additionally, even the places with no limitations did have big reductions in gatherings and foot traffic because most people are not idiots and generally took more care than usual (more on this in the next point). So the absence of stay-at-home orders did not mean that economies did well; businesses lost a lot of customers because people chose to stay away from each other.
9) It's increasingly clear that disease spread is largely driven by superspreaders. The numbers are far from precise, but something like 10% of infected people cause 80% of new infections, while perhaps 70% do not infect anybody. This is a more extreme 'clustering' than many other diseases. We don't know if there's anything particularly different about that 10% that makes this happen, in terms of physiology or immunology. But this represents an important opportunity: if those superspreading events can be contained, the epidemic may die out by itself. [The following is my speculation] I suspect this is why even weak reductions in population activity were extremely effective in suppressing the disease. And why many places have not seen surges in cases after reopening. When people took the logical step of avoiding the most crowded areas (stadiums, public transportation, bars, restaurants, etc), they effectively prevented a lot of potential superspreading events. I'd like to stress this point: it shows that even weak compliance with distancing recommendations/rules can be immensely beneficial for the whole population. This is worth keeping in mind as the lockdowns are lifted, new outbreaks happen, and plenty of people can't be arsed to obey the resulting lockdown reimposition.
10) As countries reopen, there is going to be intense debate and lobbying about what to allow. Given what we know, crowded places/events with a lot of people expelling a lot of air are probably the riskiest. An incomplete list would be: gyms, sports stadiums, concerts, university dorms & big classes, some places of worship (there seems to be a weirdly high number of reported outbreaks among choirs), nightclubs, some kinds of restaurants & bars. There's some evidence that younger kids don't get infected much and so reopening schools may be less of a concern (only moderate confidence in this claim right now). I expect places of worship will be opened sooner than ideal, so we ought to be talking to religious leaders about how best to manage the consequences of the outbreaks that will ensue.
11) As we reopen, there are going to be new outbreaks. In an even mildly competent world, we'd have built up the capacity to do lots of testing, tracing, and isolation of newly infected cases. I don't think we have done this to the degree needed in a lot of countries. Since we have not done this, a second, poorer option is cycles of shutdowns and reopenings as outbreaks are detected and controlled. Except plenty of societies are barely tolerating the first shutdown, so subsequent shutdowns seem almost guaranteed to be ignored. So what happens instead? I expect we'll see plenty of businesses change how they function for the near future till we have this under control. Some businesses may also start offering exceptions to these restrictions if customers can provide proof of immunity from antibody tests. This will essentially provide extra services to people who have immunity, creating a market for both fake test results and for people to voluntarily get infected. A while ago I mentioned that governments manage this by providing people with official 'immunity passports'. This is understandably opposed by civil liberties advocates, but we might end up with a messy private version of this instead.
12) I mentioned universities earlier and want to expand on this. A combination of factors are going to send a lot of universities - especially in the US - into financial freefall. The risk in crowding lots of people together into classes & dorms, the poorer educational experience of video conferencing, high tuition fees, immigration restrictions cutting off high-paying foreign students. and the inevitable recession-driven slashing of government funding (in the US) are all going to hit the bottom line. Also, universities have apparently been mismanaged to the extent that many do not have the financial reserves to weather these storms (if they can't even manage money, why on earth did we let the corporate world start running them?). The famously large endowments are not (according to university spokespeople) funds that can be used to manage the crisis, because money willed to the university comes with specific conditions attached. Using them to tide over general budget shortfalls apparently violates a bunch of legal agreements, ones which universities are less happy to break than say, union-negotiated job contracts and pension liabilities. The biggest universities will probably manage somehow, in part by taking in students who might otherwise have gone to lower-rung universities. At least some of those lower-rung universities may have to have to radically change or close down. Hopefully some good will come from the necessary experimentation. Teaching in the lockdown has kicked many of us out of our rut and may help improve what we do. With more support and practice, we could perhaps be teaching more students, better. But it seems likely to be a bleak few years to be an academic, especially an early-career one.
13) I've argued previously that you should ignore the headline of the day, because most science papers offer provisional results, the media communicates science badly, and you will end up misinformed. I stand by that, but feel obligated to talk about one study in the Lancet that claimed that hydroxychloroquine does not help with COVID and actually kills people instead. For obvious political reasons, this story spread like wildfire. Well, there are massive problems with that study, and not of the usual scientists-disagree-about-how-to-interpret-everything kind. There's an extremely good chance that it is a hoax and the data completely made up. Here's one valuable critique you can read: http://freerangestats.info/.../implausible-health-data-firm . Note that this does not mean that hydroxychloroquine is actually good.
14) We're likely to see more protests of all kinds soon, and not just in the US. These protests are extremely likely to spread the virus. If you argue that the goals of a specific protest are more important than the possibility of spreading the virus, be prepared to listen when a similar argument is made by those protesting for goals you dislike. Dismissing their arguments out of hand will lead to charges of hypocrisy, and people who disagree with you politically will have less reason to listen to your advocacy on any topic. In any case, we should be preparing for outbreaks in all these cities where protests happen. The sad fact, though, is that contact tracing is going to be a much harder sell when protestors view it as a way for authorities to track down and suppress political dissent. Contact tracing that maintains privacy may be vital here.
15) Slow vaccine progress continues to be made on a variety of fronts. Two of the best initiatives on that front are those by the Gates Foundation and Operation Warp Speed by the US government, both of which are spending billions to build capacity for vaccines that we do not have yet. Most of that money will end up being spent on vaccines that do not work. But if one or two work, it could save millions of lives and trillions of dollars. This is the kind of targeted, wise initiative that we need more of, and not just to deal with this virus.
------------------
In response to 2 questions about my speculation in point #9 that weak measures may be sufficient to stop superspreading:
(i) about modelling rare events
A toy model should be relatively simple to implement. If you want to get fancier, here's some resources you might find interesting/useful:
https://www.nature.com/articles/nature04153 (old & general, and already supports the basic intuition)
https://covid.idmod.org/.../Stochasticity_heterogeneity... (very new, specific to COVID)
https://epidemicsonnetworks.readthedocs.io/.../index.html (Python module for modelling epidemics on networks)
(ii) explaining my intuition behind why weak measures can stop superspreading:
I'm going to invoke some realistic numbers for this based on what we now know about COVID:
Imagine 10 people are infected. 7 of them do not pass it on; actually, let's say they *cannot* pass it on, for argument's sake. Of the remaining 3 people, 2 pass the infection on to 1 other person each. Let's say this is to a family member or someone they are closely associated with. The disease spread by these 9 people may be unaffected by distancing & lockdowns, but it only results in 2 infections.
For the disease to continue to spread, the remaining 1 person has to infect more than 8 people, since the initial 10 has to infect more than 10 or it dies out. In ordinary times, this may happen when they encounter crowds at the office, or church, or a restaurant, or on the bus, or a concert, or so on.
When people are distancing and the most crowded areas are shut down or avoided, this one infective person encounters fewer people and at lower densities. This makes them much less likely to pass it on to more than 8 people. Even if people are not strictly following the rules or the lockdown is quite mild, they may infect only 4 or 5 more. The newly infected cohort is 7 people (2 + 5), which is lower than the previous cohort. Since the same logic applies to them, over time the number of infected dies down and goes to zero.
Basically, preventing a few people from each infecting 10 people is easier than preventing lots of people from each infecting 2 people.
------------------
In response to a question about a Medium article about Covid being a 'blood-vessel disease':
It does seem to be a plausible mechanism, though the Medium title is hyperbole. There's been a couple of months of reporting on this, and the story does seem to be gaining in prominence (see this from yesterday, for example: www.sciencemag.org/news/2020/06/blood-vessel-attack-could-trigger-coronavirus-fatal-second-phase )
There's an odd angle to this story that I spent some time on. The Medium article cites only one scientific paper, so I took at look at it. Bizarrely, it shares a couple of authors with the hydroxychloroquine paper that appears to be a hoax (the one I wrote about above in point #13). That made me worry about how reliable this paper was, so I dug into that a bit. As best I can tell, the shared co-authors were not the main players in the (alleged but very likely) hoax. I'd guess they were innocent; their other co-authors on the dodgy paper were from a company that seems to have fabricated the data. It does call these doctors' judgement into question, though.
------------------
In response to a question about the role of population density and infrastructure:
I agree that density & infrastructure are likely to be very important, and probably a major reason why New York was hit so horribly. And yeah, that also implies huge differences between states, which is likely to make co-ordinating policy tougher. Low-density states are generally Republican and already relatively sceptical of scientists. If they are fortunate and escape big outbreaks, they are likely to become even less supportive of public health efforts, including vaccination when that becomes possible.
Europe basically suspended Schengen when it closed all borders, and each country chose its own path and felt the consequences of its own decisions. US states will be pursuing different strategies but won't be able to close borders, which makes the outcomes dependent partly on the policies of their neighbours. I expect this will cause a lot of friction.
1) It's happened without much fanfare, but it seems as though contact with surfaces is no longer thought to be a very important method of spreading the virus. In March, there was a lot of advocacy around using gloves, washing hands, & avoiding face touching. As more evidence has poured in, the cautions and analyses have shifted towards focussing strongly on inhalation of viruses. I have yet to see clear research on the relative risks (please tell me if you know!), but I think this is a fair summary of epidemiologists' present beliefs. I'm not saying that viruses do not spread through contact with surfaces, so continue to take reasonable precautions. But I offer this to allay the fears of friends who go to incredible lengths to sanitise everything they buy or that enters their house. Letting new acquisitions sit in the sun for a week is overkill.
2) Brazil and India have exponentially increasing case numbers despite lockdowns - in India's case, one of the most brutal in the world. The outbreaks are concentrated in some regions, so it is possible that they will get contained. But given exhaustion with the cruelly mismanaged lockdowns (at least in India), I'm doubtful they will be. And they have
20% of the world's population between them.
3) As a consequence, the situation right now is far worse than I think most people realise. Global daily deaths are slowly decreasing (currently ~3000 per day), driven by improvements in the situation in Europe and the US, which were hit worst. The news is moving on to the economy, tourism, protests, and so on as local situations seem to stabilise, and people get bored or desperate. But this apparent progress can be quickly reversed by just one or two new outbreaks that can happen anywhere, and these seed new outbreaks in turn. We do not have a single pandemic, but a patchwork. Regions/countries with outbreaks can be isolated, but the success rate needed to prevent them seeding new outbreaks is very high. Most countries have not displayed the competence needed. We are stuck in this situation till we have a vaccine.
4) As India's & Brazil's numbers rise, global daily deaths will start to increase again. We are now looking at possibly millions to even tens of millions of deaths. This probably seems unlikely to you and I hope it's totally wrong. But in March, the possibility of tens of thousands of deaths was seen by many as unwarranted pessimism, and hundreds of thousands as wild fantasy. And yet here we are. We ought to learn something from this about how unreliable gut impressions about worst-case scenarios and tail risks are. And perhaps eventually turn that insight towards another area where scientists have spent decades venting their spleens about tail risks: climate change.
5) A better argument for why millions of deaths is plausible: a few weeks ago, Spain and France did the biggest & best random testing programs run so far, helping to fill a massive gap in basic data. These found that the infection fatality rate is about 1%, just as epidemiologists have been saying since at least March. Remember that infection fatality rate is the % of people who ever got infected that die, which is the number we are most interested in. Most reports have been about the case fatality rate, which leaves out all the people who got infected but did not know about or report it; this varies a lot based on medical system and reporting practices. Also, about 5% of those countries had been infected (i.e. had antibodies) at the time. If the virus were to continue to spread, you would not get 20 times as many deaths, but you would get very large numbers that are in line with those that basic epidemiological models predicted months ago. Apply that logic and the basic numbers to other parts of the world and you gets millions to tens of millions.
6) A particularly worrisome pattern: there are many more young people infected and hospitalised in India and some other countries than was expected. There's multiple reasons why this may be, such as exposure patterns and data biases. There are more scary possibilities but right now no real evidence for them. But even so, outbreaks among young people are a massive threat to countries with much younger populations, where the hope was that the vulnerable elderly could be isolated while the young slowly return to work.
7) Since I'm thoroughly sick of the endless debate around Sweden and its tactics, allow me to point out stories from other countries that are not discussed much. Take Mongolia and Vietnam, which have had zero deaths between them with a combined population of 100 million. Zero. And they share a border with China! Senegal, though further away, has had about 40 deaths in a population of 31 million. Ghana: about 35 deaths among 16 million people. Ethiopia: 12 deaths out of 115 million. All these countries are relatively poor and lack the capacity of European and American healthcare systems, in terms of manpower, training, and technological sophistication. What they share is that they took action in January, while more developed countries did nothing. I'll add that they are also younger, but I think that is a less important factor. Ghana and Ethiopia are noteworthy, because I understand they implemented better contact tracing than most of Europe or the US. Ghana also tested large numbers of people by using pooled testing, an old method I discussed in the very first of these posts in March. Germany and India have also been using the same strategy, which should have been employed months ago. I was personally terrified about outbreaks in developing countries, and want to highlight that many of them have outperformed the wealthiest countries to an impressive degree, one that ought to shock us. They may yet suffer badly, but they have done well so far.
8) Reopening in many countries is politically inevitable now and justified in many cases. Did the lockdowns work? It's a question that's going to be contested very strongly because of the political and economic implications. But please keep in mind that this is not exactly a yes/no question. There was not a single type of 'lockdown'. Instead, there was a wide range of activity restrictions, ranging from stay-at-home with almost no exceptions (China, India, Italy, France) to limitations on gathering places such as restaurants & movie theatres but not much else (Switzerland) to essentially no legal limitations, just recommendations (Sweden, Ethiopia). There were successes in countries in all these categories. So a case could be made that the strictest stay-at-home orders were not needed, at least in areas without high population densities. But let's put that in context. Strict restrictions were entirely justifiable at the time given the limited information we had and the very real threat of having healthcare systems overwhelmed (as happened in northern Italy). Shutdowns were protection against very real tail risks. Additionally, even the places with no limitations did have big reductions in gatherings and foot traffic because most people are not idiots and generally took more care than usual (more on this in the next point). So the absence of stay-at-home orders did not mean that economies did well; businesses lost a lot of customers because people chose to stay away from each other.
9) It's increasingly clear that disease spread is largely driven by superspreaders. The numbers are far from precise, but something like 10% of infected people cause 80% of new infections, while perhaps 70% do not infect anybody. This is a more extreme 'clustering' than many other diseases. We don't know if there's anything particularly different about that 10% that makes this happen, in terms of physiology or immunology. But this represents an important opportunity: if those superspreading events can be contained, the epidemic may die out by itself. [The following is my speculation] I suspect this is why even weak reductions in population activity were extremely effective in suppressing the disease. And why many places have not seen surges in cases after reopening. When people took the logical step of avoiding the most crowded areas (stadiums, public transportation, bars, restaurants, etc), they effectively prevented a lot of potential superspreading events. I'd like to stress this point: it shows that even weak compliance with distancing recommendations/rules can be immensely beneficial for the whole population. This is worth keeping in mind as the lockdowns are lifted, new outbreaks happen, and plenty of people can't be arsed to obey the resulting lockdown reimposition.
10) As countries reopen, there is going to be intense debate and lobbying about what to allow. Given what we know, crowded places/events with a lot of people expelling a lot of air are probably the riskiest. An incomplete list would be: gyms, sports stadiums, concerts, university dorms & big classes, some places of worship (there seems to be a weirdly high number of reported outbreaks among choirs), nightclubs, some kinds of restaurants & bars. There's some evidence that younger kids don't get infected much and so reopening schools may be less of a concern (only moderate confidence in this claim right now). I expect places of worship will be opened sooner than ideal, so we ought to be talking to religious leaders about how best to manage the consequences of the outbreaks that will ensue.
11) As we reopen, there are going to be new outbreaks. In an even mildly competent world, we'd have built up the capacity to do lots of testing, tracing, and isolation of newly infected cases. I don't think we have done this to the degree needed in a lot of countries. Since we have not done this, a second, poorer option is cycles of shutdowns and reopenings as outbreaks are detected and controlled. Except plenty of societies are barely tolerating the first shutdown, so subsequent shutdowns seem almost guaranteed to be ignored. So what happens instead? I expect we'll see plenty of businesses change how they function for the near future till we have this under control. Some businesses may also start offering exceptions to these restrictions if customers can provide proof of immunity from antibody tests. This will essentially provide extra services to people who have immunity, creating a market for both fake test results and for people to voluntarily get infected. A while ago I mentioned that governments manage this by providing people with official 'immunity passports'. This is understandably opposed by civil liberties advocates, but we might end up with a messy private version of this instead.
12) I mentioned universities earlier and want to expand on this. A combination of factors are going to send a lot of universities - especially in the US - into financial freefall. The risk in crowding lots of people together into classes & dorms, the poorer educational experience of video conferencing, high tuition fees, immigration restrictions cutting off high-paying foreign students. and the inevitable recession-driven slashing of government funding (in the US) are all going to hit the bottom line. Also, universities have apparently been mismanaged to the extent that many do not have the financial reserves to weather these storms (if they can't even manage money, why on earth did we let the corporate world start running them?). The famously large endowments are not (according to university spokespeople) funds that can be used to manage the crisis, because money willed to the university comes with specific conditions attached. Using them to tide over general budget shortfalls apparently violates a bunch of legal agreements, ones which universities are less happy to break than say, union-negotiated job contracts and pension liabilities. The biggest universities will probably manage somehow, in part by taking in students who might otherwise have gone to lower-rung universities. At least some of those lower-rung universities may have to have to radically change or close down. Hopefully some good will come from the necessary experimentation. Teaching in the lockdown has kicked many of us out of our rut and may help improve what we do. With more support and practice, we could perhaps be teaching more students, better. But it seems likely to be a bleak few years to be an academic, especially an early-career one.
13) I've argued previously that you should ignore the headline of the day, because most science papers offer provisional results, the media communicates science badly, and you will end up misinformed. I stand by that, but feel obligated to talk about one study in the Lancet that claimed that hydroxychloroquine does not help with COVID and actually kills people instead. For obvious political reasons, this story spread like wildfire. Well, there are massive problems with that study, and not of the usual scientists-disagree-about-how-to-interpret-everything kind. There's an extremely good chance that it is a hoax and the data completely made up. Here's one valuable critique you can read: http://freerangestats.info/.../implausible-health-data-firm . Note that this does not mean that hydroxychloroquine is actually good.
14) We're likely to see more protests of all kinds soon, and not just in the US. These protests are extremely likely to spread the virus. If you argue that the goals of a specific protest are more important than the possibility of spreading the virus, be prepared to listen when a similar argument is made by those protesting for goals you dislike. Dismissing their arguments out of hand will lead to charges of hypocrisy, and people who disagree with you politically will have less reason to listen to your advocacy on any topic. In any case, we should be preparing for outbreaks in all these cities where protests happen. The sad fact, though, is that contact tracing is going to be a much harder sell when protestors view it as a way for authorities to track down and suppress political dissent. Contact tracing that maintains privacy may be vital here.
15) Slow vaccine progress continues to be made on a variety of fronts. Two of the best initiatives on that front are those by the Gates Foundation and Operation Warp Speed by the US government, both of which are spending billions to build capacity for vaccines that we do not have yet. Most of that money will end up being spent on vaccines that do not work. But if one or two work, it could save millions of lives and trillions of dollars. This is the kind of targeted, wise initiative that we need more of, and not just to deal with this virus.
------------------
In response to 2 questions about my speculation in point #9 that weak measures may be sufficient to stop superspreading:
(i) about modelling rare events
A toy model should be relatively simple to implement. If you want to get fancier, here's some resources you might find interesting/useful:
https://www.nature.com/articles/nature04153 (old & general, and already supports the basic intuition)
https://covid.idmod.org/.../Stochasticity_heterogeneity... (very new, specific to COVID)
https://epidemicsonnetworks.readthedocs.io/.../index.html (Python module for modelling epidemics on networks)
(ii) explaining my intuition behind why weak measures can stop superspreading:
I'm going to invoke some realistic numbers for this based on what we now know about COVID:
Imagine 10 people are infected. 7 of them do not pass it on; actually, let's say they *cannot* pass it on, for argument's sake. Of the remaining 3 people, 2 pass the infection on to 1 other person each. Let's say this is to a family member or someone they are closely associated with. The disease spread by these 9 people may be unaffected by distancing & lockdowns, but it only results in 2 infections.
For the disease to continue to spread, the remaining 1 person has to infect more than 8 people, since the initial 10 has to infect more than 10 or it dies out. In ordinary times, this may happen when they encounter crowds at the office, or church, or a restaurant, or on the bus, or a concert, or so on.
When people are distancing and the most crowded areas are shut down or avoided, this one infective person encounters fewer people and at lower densities. This makes them much less likely to pass it on to more than 8 people. Even if people are not strictly following the rules or the lockdown is quite mild, they may infect only 4 or 5 more. The newly infected cohort is 7 people (2 + 5), which is lower than the previous cohort. Since the same logic applies to them, over time the number of infected dies down and goes to zero.
Basically, preventing a few people from each infecting 10 people is easier than preventing lots of people from each infecting 2 people.
------------------
In response to a question about a Medium article about Covid being a 'blood-vessel disease':
It does seem to be a plausible mechanism, though the Medium title is hyperbole. There's been a couple of months of reporting on this, and the story does seem to be gaining in prominence (see this from yesterday, for example: www.sciencemag.org/news/2020/06/blood-vessel-attack-could-trigger-coronavirus-fatal-second-phase )
There's an odd angle to this story that I spent some time on. The Medium article cites only one scientific paper, so I took at look at it. Bizarrely, it shares a couple of authors with the hydroxychloroquine paper that appears to be a hoax (the one I wrote about above in point #13). That made me worry about how reliable this paper was, so I dug into that a bit. As best I can tell, the shared co-authors were not the main players in the (alleged but very likely) hoax. I'd guess they were innocent; their other co-authors on the dodgy paper were from a company that seems to have fabricated the data. It does call these doctors' judgement into question, though.
------------------
In response to a question about the role of population density and infrastructure:
I agree that density & infrastructure are likely to be very important, and probably a major reason why New York was hit so horribly. And yeah, that also implies huge differences between states, which is likely to make co-ordinating policy tougher. Low-density states are generally Republican and already relatively sceptical of scientists. If they are fortunate and escape big outbreaks, they are likely to become even less supportive of public health efforts, including vaccination when that becomes possible.
Europe basically suspended Schengen when it closed all borders, and each country chose its own path and felt the consequences of its own decisions. US states will be pursuing different strategies but won't be able to close borders, which makes the outcomes dependent partly on the policies of their neighbours. I expect this will cause a lot of friction.
