In writing a reply to Zvi’s recent post on Covid-19 predictions I realized I had been procrastinating on writing out my thoughts on Covid-19 in full. In this post I will explain in detail how I think about the Covid-19 countermeasures for the next few months, and explain why I think all this.

Disclaimer: my predictions are among the most pessimistic (and speculative) of the ones I've run into. Having expectations that COVID-19 will be worse than people are thinking so far can and does have negative effects on your mental health, so stop reading, now.

I’d love to be proven wrong on all of this.

What is our long term goal?

There has been a lot of discussion on the impact of countermeasures on the spread of Covid-19. However, most of this has been relatively unhelpful in trying to make predictions on longer timescales - say, until March 2021. For this reason I want to first figure out what plausible scenarios we have for the long term - i.e. what situations would be stable. I think there are three main contenders.

  • We establish group immunity, and the virus is no longer a great risk.
  • We reduce the incidence rate to such a low level that we can prevent the spread by actively intervening in every case (for example through contact tracing, isolating only people who have been exposed).
  • We (permanently) change our lifestyle to one with reduced social contact, and we make sufficiently many countermeasures against Covid-19 permanent to reduce R0 to 1 or below.

Some countries are currently aiming for option number 2 (for example South Korea, as far as I know). I think this places serious strain on globalization, but I must confess I haven't looked into this all that much. I think experts are saying it is a near certainty that Covid-19 will become endemic, so this approach would require constant vigilance to prevent new cases. If it is possible to turn this approach into a permanent state of affairs I would love to know more about it, but for now I'd like to ignore it. It also sounds very difficult in places like the US, with approximately 1,189,003 active cases today.

Option number 3 is the doom scenario economists are talking about. Entire industries will have to adapt (or, more likely, collapse). We would, as a species, be cutting into our growth to survive this virus. Most of the discussions I've had are about the (lack of) desirability of this scenario versus option 1. I personally think a lot of the severe countermeasures we are currently taking are unsustainable, ruling out option 3 (see for example the dramatic US unemployment numbers).

For the rest of this post I will discuss only option 1. For the record: there is some overlap between options 1 and 3, in that the threshold for group immunity depends strongly on R0, which can be brought down by changes in our way of life. In the section on 'the R0 scale' below I will go into this in a bit more detail, but for now I am assuming 'group immunity' means that somewhere between 20% and 70% of the population has gained immunity to Covid-19.

How do we get group immunity?

To the best of my knowledge, there are currently two ways. Either people get exposed to the virus, thereby developing immunity, or we create a vaccine. In the first case it is likely millions worldwide will die - Zvi gives the estimated IFR (Infection Fatality Rate) at 0.5%-1%, and it plausibly goes up if our medical systems get overwhelmed. But even if this stays under control, 0.5% of over 20% of the population is still 78 million people (or 328,000 in the US).

The alternative is a vaccine. This takes effort, funding and time to develop, although personally I am only effected by the 'time' consideration. Some quick googling reveals that an optimistic length of time to develop a vaccine is about 1-2 years. Sticking with the optimistic lower end of that prediction, I started looking for predictions on Covid-19 for March 2021 about two months ago. The question I was now trying to answer is "how do we manage Covid-19 until approximately March 2021, in the hope that we have a vaccine by that time (or can extend our approach a few more months if not)?".

Quarantine, and the R0 scale

Viewed through the lens of the above question, what we really need is a way to stall Covid-19 for about a year. If we can keep everybody alive and healthy through this period of time we can plausibly return to life as normal. Based on the post The Hammer and The Dance, the most realistic strategy seems to be to implement sufficiently many countermeasures to keep R0 at 1 (or, technically, oscillating around it), which is the point that gives us maximum quality of life while keeping the virus in check. The problem is that I don't think we can do this, and certainly not for a full year.

It is currently an open question how big the impact of individual countermeasures exactly are on R0, and therefore also which ones can be relaxed while which ones have to remain enforced to control 'The Dance'. To still get some rough idea, I personally think about something I call "the R0 scale". We know that currently in many places across the world R0 is close to 1, that in the brief period of serious public response to the initial outbreak it probably dipped as low as 0.7, and it peaked around 2.5-3 when people lived their lives as normal. This means that we should place our measures on a scale of "a serious quarantine" at 0.7, via "life as you are experiencing it right now" somewhere around 1, to "life as normal" around 2.5. Since our threshold for 'acceptable' is at R0=1, this suggests to me that 'The Dance' will look a lot more like 'a full quarantine, but with a few restrictions lifted' than like 'restoring social contact, but wash your hands and wear a face mask'.

As I said above this is an open question, and my conclusion is mostly guesswork. Zvi pointed out that risks follow a power law, so maybe we can get almost all of the reduction in R0 with almost none of the measures. But personally I am skeptical of this idea.

That which doesn't change

...stays the same. In March and April many places across the world have gone into quarantine to prevent the spread of Covid-19. I support that decision (in fact, I would have liked it if everybody responded faster). If, at some point in the future, we have the same number of contagious people, and are not at an appreciable fraction of group immunity, it will at that point again be a solid decision to go into quarantine (or to extend it). There are other considerations that confound this decision (prolonged quarantine has non-linear effects on the economy, a lot of companies only have a few months worth of liquidity, for example), but from a medical point of view the argument is sound. If the number of contagious people is the same as before, and you revert the Covid-19 countermeasures, the exponential growth will pick up right where it left off last time. This is as true in March as it will be in November.

This is why I personally think the idea of a 'second peak' is flawed or misleading. Covid-19 growth is subject to a control system made of human response. We can, in theory, produce as few or as many peaks as we desire by modulating our countermeasures. Conversely, relaxing measures will do exactly this (create new peaks, when we go over R0=1). It's not like the virus will respond differently to increased social contact a month from now than it did two months ago. This is why the timeline for the vaccine is so important - all the other countermeasures we currently have are only stalling for time, they are not exit strategies. In particular, I think this time scale is the only relevant one for our long term plans. Multiple people in my social circle are making plans for the summer holidays, or the fall semester, under the assumption that we will have Covid-19 under control by then and the countermeasures will be significantly relaxed. However, I don't see what will have changed between the situation as it is right now and as it will be in August. Why and how will things have changed?

So will all this work?

No. Having considered all of the above, I think it is exceedingly unlikely that we will be able to maintain a state sufficiently similar (i.e. R0=1) to our current quarantine for almost a year. The impact on the economy is devastating, unemployment numbers are skyrocketing and people are unable to endure being cooped up for that long. (Again) Zvi pointed out that it is highly suspicious that currently R0 is so close to 1, and that this is more than likely to be a feedback system. I agree, it is a feedback system of people balancing their fear of Covid-19 and wish to comply with government orders against their reluctance to stay at home/cut back on social activities/miss out on work, mediated by the official reports and statistics. But I expect the cost of staying at home to rise dramatically in time (due to mental health, lack of income, etc.), while the risk of Covid-19 stays roughly constant (and the fear of it might even go down). In short, I think the current balance is not sustainable.

Which puts me at a serious impasse. The text above is far from rigorous, and there might be any number of creative solutions that I have not considered. But personally I think "maintain The Hammer and The Dance until we have a vaccine" is one of the most realistic-sounding long-term approaches to Covid-19 (mostly because a vaccine is our only exit strategy, besides letting the virus run rampant). And I think it will fail dramatically, because such a quarantine is not sustainable for that long.

There is a lot more I would like to say about all of the above, most of which I have very low confidence in but would love to have some discussion on (in particular the 'second peak' and 'the R0 scale'). I have much higher confidence in any of the individual steps than in the conclusions, and I hope that the discussion can be kept at the same coarse-grained level of detail as the one that I have tried to keep for this post.

New Comment
11 comments, sorted by Click to highlight new comments since:

I think you dismiss the non-lockdown options too glibly. Like many, you seem trapped in the dilemma "lockdown and kill the economy vs no lockdown and kill the people". You, and many others, need to have a close look at what countries like Taiwan (and others) have done - no lockdown and few deaths.

Possibly there is an element of western arrogance in the way many western countries refuse to learn from Asian countries that have been far more successful in keeping their economies open and deaths low. Two key elements that are surprisingly effective: ubiquitous use of face masks, and the use of cheap, simple, rapid metrics to exclude people from schools, shops, workplaces, and public transportation.

Simple metrics like checking for cold/flu symptoms and taking temperatures are not infallible ways to determine if someone has the SARS-CoV2 virus. But they are very useful, and can be done at a rate that dwarfs the possible rate of PCR tests. As a result you can actually gather more information across the whole society, and the information is more current.

Lockdown is also ruinously expensive and unsustainable. In my simulations maybe $20M/life saved, $300K/capita over a year.

Remember we need only get R0(eff)< 1. We do not need to get it to zero. That means a bit more than a 50% reduction, maybe 60% from the base rate ~2.5.

The level of infection at which "herd immunity" occurs is IMHO very much up in the air. The simple SIR models tend to overstate the level needed, because they generally don't take into account the fact that in epidemics the super-spreaders get taken out, one way or another, quite early, and the remaining more cautious and safer people have a much lower effective R0. IMHO it may be as low as 15% or as high as 50%, but unlikely to be as high as 65%. Epidemiologists talk about epidemics dying out for mysterious reasons, and it is speculated it is something about the microstructure of society, like superspreaders and more generally the variance of infectivity/susceptibility of people and groups, that is responsible.

I suspect that one major difference with Taiwan and other East Asian countries is that they have been able to effectively stop community spread before it became endemic. South Korea I know did enough contact tracing that almost every person exposed has been quarantined. Taiwan only had around 500 cases, so that I presume was the same solution (I haven't investigated it). Essentially, I'm saying that it's too late for the US or Europe to be like non-China East Asian countries. As for China, their solutions would not be able to get political support (and are arguably worse than the virus itself).

Remember we need only get R0(eff)< 1. We do not need to get it to zero. That means a bit more than a 50% reduction, maybe 60% from the base rate ~2.5.

Currently R0 ~= 1, so I'd assume that any fewer measures would result in R0 > 1. One important caveat though is that many of the measures are probably minor enough that we might be able to effectively get down to R0 ~= 1 by just doing some of the measures, like wearing masks and avoiding crowded-rooms-with-singing.

Thank you for your comment! I'd like to briefly clarify that I don't consider the "lockdown versus kill the people" question a dilemma - I'm not trying to propose policy, just attempting to make realistic predictions for the next few months.

I think going for the approach you suggest ('option 2') is unrealistic in most western countries, and that the countries where this strategy worked had unique circumstances that worked in their favour.

As gbear605 points out, it is a lot more difficult to revert to this strategy when the disease is endemic, compared to when the number of active cases is in the several hundreds. In the post I link to an estimate of 1.1 million active cases of Covid-19 in the US today. One of the bigger weak links in the non-quarantine approach is that, when people test positive for cold/flu symptoms, there needs to be some plan or support in place to thoroughly isolate them for up to two weeks. At lower numbers this can plausibly handled by hospitals or nursing homes (which has been a big part of South Korea's method), but at up to a million cases this is unrealistic. In effect this would be akin to a lockdown with some extra steps.

Another advantage that South Korea, Taiwan and Singapore (as far as I know the biggest success stories of this method) had is that they are geographically isolated. I imagine this cuts down on the threat of re-infection from outside the country, and also why it is so much more difficult to prevent Covid-19 from becoming endemic in the US.

Widespread screening for elevated temperatures and cold/flu symptoms sounds like a very clever (and cost-effective!) method to combat the virus, if we also have a plan ready for people who test positive. But I don't think it can be the success story in western countries that it is in some Asian countries. We either missed our window and let Covid-19 grow too much, or we never had a window to begin with.

As for your later two points, I believe I addressed those in the original post. I think bringing R0 down to around 1 and keeping it there is prohibitively taxing, in multiple ways, and that even slight relaxation of our response will already have severe consequences. We should be thinking on the R0 scale, which runs from about 0.7 to about 2.5-3. Also I explicitly mention that I am fine with leaving the level at which we achieve herd immunity open for debate (I give 20% as a somewhat lower bound, based on estimates that this exposure level has already been reached in NYC).

I still think you dismissed the possibility of containing coronavirus too easily.

If we look at coronavirus deaths per 1M population:

  • Spain, UK -- 600
  • Italy -- 550
  • France, Sweden -- 450
  • Ireland, Netherlands -- 350
  • USA -- 300

...yeah, seems like a consistent pattern: if you are a Western country, you cannot avoid tens of thousands of deaths. That's the price of not living on a tiny isolated island.

But wait! Keep reading:

  • Canada, Switzerland -- 200
  • Denmark, Germany -- 100
  • Austria -- 75
  • Finland -- 60

Somehow these countries have better results. Finland, Denmark, and Sweden seem to belong to the same reference group; it keeps surprising me how the one with the worst results among them somehow became the internet example of a Western country dealing with the coronavirus successfully.

German language seems to provide some extra immunity against coronavirus: Germany, Austria, and partially Switzerland. And these countries are not islands -- they actually have less of a shoreline than the countries above them.

Now let's look at Eastern Europe countries that are members of European Union -- they have (had, before the pandemic) free borders with Western countries, and many people regularly move between the countries, e.g. because they work abroad. In other words, also not tiny isolated islands.

  • Romania -- 70
  • Hungary -- 55
  • Estonia, Slovenia -- 50
  • Czechia, Poland -- 30
  • Croatia, Lithuania -- 25
  • Bulgaria -- 20
  • Latvia -- 15
  • Slovakia -- 5

I am from Slovakia. I suppose I should get a "if you want to survive coronavirus, ask me how" t-shirt. ;)

Here is the short history: the first confirmed coronavirus infection case was on March 6; let's call it "Day 1". March 10 ("Day 5") -- schools, universities, and kindergartens in the capital city were closed. March 12 ("Day 7") -- lockdown started, and border control was reinstated; only people who had residence or employment in Slovakia were allowed to enter. March 15 ("Day 10") -- face masks mandatory in transit and shops. March 25 ("Day 20") -- face masks mandatory everywhere. April 8 - 14 ("Days 39 - 45") -- curfew except for work, shopping, and nature. April 22 ("Day 53") -- gradual relaxation of quarantine measures started.

As of today, the situation is halfway back to normal: the schools are gradually opening this week, most services are available with some limitations (washing hands, wearing face masks, limited number of people in the same room). In a population of 5.5 million, we had 1522 total confirmed cases and 28 total deaths. During the last 40 days, the number of new cases was less than 5 per day on average.

My conclusion is that good results are possible when the government reacts fast. (And not only the state government. The schools in the capital city were closed by the city government on Day 5. Some shops required hand disinfection at entry and limited the number of customers on their own initiative during the first week.) Things like hand disinfection and simple face masks are relatively cheap. As long as the number of cases is low, test everyone they were in contact with.

Of course, if you start from the "nothing can be done" perspective, call your (lack of) strategy "herd immunity", and insist that face masks are worthless unless they are N95... then you get an order of magnitude worse results, and you should still consider yourself lucky, I suppose.

Thank you for your comment. I don't think we disagree - Slovakia (and other European countries) have done extremely well by acting quickly. I also fully support washing hands, wearing face masks and being smart about social contact. I think you are responding to my sentence

[...] this suggests to me that 'The Dance' will look a lot more like 'a full quarantine, but with a few restrictions lifted' than like 'restoring social contact, but wash your hands and wear a face mask'.

I'm sorry for the confusion. The situation you describe sounds more like my scenario 3 than my scenario 2, and I think I explained poorly where I draw the line in my quoted statement above. Going by wikipedia, the most recent round of relaxations in Slovakia still sounds far from life as normal to me. The maximum occupancy set at shops is up to 1 person per 15 square meters, which is 25% of what it is in normal times. I imagine similar concerns apply to offices, but I can't find how many people are back to working at the office. The opening of schools happened only this Monday, so it really is too early to tell what the impact of that will be. Zvi voices some concerns.

Lastly, my entire goal was to try and talk about relative impact, and give perspective to the magnitude of the measures we can expect going forwards. I don't see where I have mistakenly given absolute statements on effectiveness of measures (in fact I only mentioned face masks once, without making any statement for or against them in the OP), but if you point them out I would be happy to change them.

On the second reading, yeah, I also think we mostly agree. My comment made more sense to me (as a reaction to you) when I was writing it than it does now... I guess that's an inherent risk of commenting past midnight; sorry for that.

The line between scenarios 2 and 3 would be difficult to draw, because most countries probably do a bit of both. I suppose by now almost everyone tries to do tracking, testing, and quarantine... as much as the number of active cases permits logistically. I also suppose that by now almost everyone encourages hand washing, and at least some degree of social distancing. (The face masks seem to remain controversial in some countries, for reasons beyond my understanding. Unless this information is obsolete, because things change so quickly.)

There also seem to be things not discussed publicly. I've heard that some countries adopted an (unwritten?) rule that in care homes, old people with COVID-19 symptoms should not be sent to hospitals, but merely given painkillers, to prevent hospital overcrowding. Yeah, reliable source needed.

The permanent lifestyle changes do not have to be as bad as it sounds. Some of them may fall into category "a bad situation forced us to explore new options, and some of them actually turned out to be improvements".

For example, I really enjoy the possibility of working from home, which otherwise would not be possible. I also wasn't sure whether my two little kids would allow me to work undisturbed, which is why I didn't even try negotiating with my employer. Now that I tried it, and found a solution for the related problems, I feel comfortable about it. This knowledge is irreversible; not just for me, but for thousands of people. Many who were reluctant to work from home are now reluctant to return to the open-space offices. Could this lead to a permanent change in the industry?

The limitations put on shops made me experiment with online shopping. Previously, I was aware that it exists, but I haven't tried it. I simply bought groceries almost every day on my way back from work. Now I learned to buy for 3 days in advance, and for a purchase of this size it makes more sense to order things online (no need to carry heavy stuff, discount on transport). I learned to cook from leftovers. Some of these habits will probably stick. Also, some shops and restaurants that didn't do it before, now started doing home delivery. (You mentioned 25% of supermarket capacity, but in real life it doesn't feel like an issue -- either I am lucky, or people generally started to order stuff online and shop more strategically, so the new supermarket capacity remains sufficient. I spend less time waiting in a line than I did before.)

Avoiding traffic made me always check on Google Maps how far something is by feet. Surprisingly, many things are closer than I assumed. I live in the center of the city, so "20 minutes by feet" actually covers quite a lot. Another possibly permanent, slightly-R0-reducing change.

By the way, I suspect that thinking about R0 as one number is somewhat misleading. I believe that a small subset of people/activities are superspreaders, so maybe "R0 = 2" could easily become "R0 = 1" by preventing a small number of activities, with small impact on most people. Yes, it is a political problem; the superspreaders will be quite vocal about their freedoms. With sufficient tracking and testing, we could put the superspreaders in quarantine after infecting their first hundred victims, thus preventing them from infecting thousand more. There could be a cultural change making superspreading events less popular.

With regards to second peak, I don't know what is the impact of season. Maybe the thing that contributed most to slowing down coronavirus was the summer. (By warming up the air; by giving people more vitamin D; or possibly some other mechanism, or all of them combined.) If that is the case, the second peak will come at autumn. We should spend the summer having as many social activities as we can, while we still can.

I'm happy to hear that some of these changes have been unexpectedly positive for you! Personally I already did a bunch of these things (shop for one week's worth at a time, have days working from home, order online). To offer a bit of a peek at the flip side: I work in mathematics, which is uniquely suited for working at home (there's a modern joke that to do mathematics all you need is pen, paper, a bottle of water and a supercomputer), yet 2 of the 11 colleagues in my group have suffered burnouts since March from the added stress of having to look after their households. We are considering going back to 20% office capacity soon in staggered shifts, which while nice still means we won't have a chance to talk or work together in practice. Obviously this is exactly the point, but I want to note that this is a far cry from normal. My productivity at the moment is at an all time low, and several of my other friends have already heard that if this situation continues for much longer they will be let go from their jobs. In this sense I think this is unsustainable, or at the very least a serious hit to our global growth and productivity.

I have absolutely no quantitative guess what the impact of superspreaders is, and it would be amazing if we could stop them quickly. I think Zvi also pointed out that superspreaders get eliminated quickly in a pandemic, one way or another (and 'having the disease, surviving and then becoming immune' counts as the other).

I thought that the current spread of Covid-19 in warmer countries (Brazil, India) was evidence against the virus being very susceptible to temperatures, but there are a lot of confounders. If you know of any good summary of the current knowledge on this please let me know, I am very interested in this (and it would likely change my predictions massively).

I gave up on trying to model the situation. According to available data, the number of cases grows linearly -- faster in some countries, slower in other countries, but almost everywhere linearly; approximately the same number of people infected each day. This doesn't make sense to me. This stuff is supposed to be exponential, right?

Linear growth could make sense for a small country, such as Slovakia, if the internal situation is under control, and the number of infections is proportional to the number of people crossing the border. But what about bigger countries? What about those that do not have the situation under control?

A friend proposed a hypothesis that for countries like USA the reported number of infections is simply the number of people that were tested on given day, which is just a small fraction of the true number of infections. It makes sense to assume that the number of people tested each day is constant. But if the hidden growth was truly exponential, the difference between the true number of cases and the official number of cases would soon become visible... and that didn't happen.

Another hypothesis is that politicians are already doing the "dance" as a consequence of their incentives: when the number of cases grows too quickly, there is a pressure to do something about it, and when it stops growing, there is a pressure to relax the measures, so the result is linear growth. Doesn't sound plausible either: the incubation period is a week, so the reactive policy should lead to a sine wave instead of linear growth.

tl;dr -- I don't know; any hypothesis sounds wrong

The seasonal hypothesis would make sense if it's not the absolute temperature that matters, but rather the relative sunshine, compared to the rest of the year. That is, the Sun does not have an impact on viruses directly, but rather on people, like it creates a yearly metabolic cycle, with different resistance to diseases at different parts of the cycle. But this is just something I made up, and I have no idea whether there is any support for this in biology.

Sorry about your situation. Could you perhaps try to have Skype calls with your colleagues during the work time? I mean, when you are at work, you probably take breaks and socialize. You can do the same at home, too. People working from home often forget to take breaks.

[1] For scenario 1(herd immunity) to be a viable option we need that the virus doesn't mutate too fast and that that the reinfection rate is low enough. To my knowledge there is still a large uncertainty about either of those conditions.

[2] Some people in my circle are suggesting that we get rid of handshakes on a permanent basis, arguing that the expected spread of not only covid but also other regular germs. I am worried about costs associated with increased isolation but acknowledge that it would save lives.

"If, at some point in the future, we have the same number of contagious people, and are not at an appreciable fraction of group immunity, it will at that point again be a solid decision to go into quarantine (or to extend it). "

I think for many people the number of infections at which this becomes a good idas has increased as we have more accurate information about the CFR and how quickly realistic countermeasures can slow down an outbreak in a given area, which should decrease credence in some of the worst case scenarios many were worried about a few months ago.

I agree completely. However, I think the amount it has gone up is critical here. A lot of the countermeasures and increased preparation are linear countermeasures against an exponential threat - maybe a region that could previously only handle 1000 ICU patients can now take care of 2000, but if R0 is significantly above 1 (lets say 1.5) this only buys you about one and a half week. I think this topic deserves its own entire post at some point, and I didn't want to get bogged down in details in the section on "What doesn't change", but if the true rule is "if under X circumstances in March it was smart to go into lockdown, it is November smart to go into lockdown 2 weeks after seeing X" my conclusions are still the same.

I might write that full post sometime on this and more back-and-forth, if people are interested. I made serious concessions to brevity above.