Expected, better, and worse cases

19 March 2020

Apologies for no update yesterday.  We’re discovering that home schooling three children and keeping the house running is a 12-hour/day job, and are having to manage work and a bit of exercise in the early and late hours.  Hopefully we’ll get more efficient over time but updates might not be daily.

Today’s update is relatively brief.

Many friends have sent fascinating papers, articles, resources, questions, and observations.  Thank you and keep them coming!

Question: What’s are the arguments against the current “expected case”?

If you’ve been following these updates for a while, you will likely have concluded (mostly correctly) that I subscribe to what is emerging as a kind of received wisdom “expected case.”  (I’ll go on to describe this in a moment.) 

But given the speed with which many policymakers and governments have swung from relative inaction to adopting a set of increasingly stringent control measures–no doubt from a mixture of expert advice and political considerations–and given the extreme economic and human impact of these measures, it’s worth asking (as several friends have been asking) the following question: What are the best arguments in the other direction — that argue that the impact will be less severe than we think; that less stringent control measures are required or that control measures are required for a shorter period of time; etc.?

In the meantime, here is a high-level, hand-waving summary of how I’ve tried parse out my own beliefs and the relatively likelihood of each. 

Even as I write this, my thoughts are evolving quickly on this; what I’ve written here represents what I thought as recently as 48 hours ago; but as I engage further with the best counterarguments, I’ll likely end up reducing p(expected case) and increasing p(less bad case).

I should also add a few methodological points as a prefix. 

  • I try to behave as a good Bayesian, determining my priors, assigning probabilities to different scenarios, and then updating based on new information.  For the technically-minded, these are subjective or Bayesian probabilities, not frequentist probabilities.  
  • I’m strongly influenced by Philip Tetlock’s work on forecasting, best summarized in his outstanding book Superforecasting.  Most relevant to my thinking here is the puzzle of what base rates to use in such a rare situation as COVID-19, where we don’t know the extent to which past examples are a good guide as to what to expect.  
  • Finally, you’ll note that I group together a number of very different topics within each case: disease progression, health impact, government reaction, economic impact, etc.  There’s a different approach one can take to forecasting, which is to string together conditional probabilities; but I think the interaction of these elements is so complex and non-linear, with lots of unknowns and lots of feedback loops, that this just gives false precision.So with that, I describe three cases with my subjective probabilities.

1. p=60% Expected case. 
In many countries (including most of Europe, UK, US) we face 4-12 weeks of severe and (in some countries) escalating control measures.  After an initial peak that stresses emergency services, this begins to bring the rate of infection down and allows health services time to build capacity.  The virus persists after that and we face a 6-12 month further tension between relaxing control measures and seeing higher infection rates.  Some countries can’t or won’t sustain long-term controls and see second and perhaps further waves; so we may see-saw back and forth between significant and more relaxed controled measures.  The economic impact is severe for several months and there may be further waves of panic that drive markets lower.  We reach 25-40% attack rates with infection fatality ratios (IFRs, which unlike CFRs are based on the actual rate of infection, not the confirmed rate) of 0.5-1.0%.  Then it mitigates somewhat, and 3-9 months from now we begin to return to a “new normal” where most economic activity returns, albeit with some sectors permanently impacted. In the meantime, many businesses may have gone bankrupt, many individuals are out of work, some businesses are nationalized and/or bailed out, etc.  While the world’s productive capability is not significantly diminished in the medium-term, the massive fiscal stimulus and expansion of government balance sheets may store up inflation (possibly asset price instead of monetary), and will cause huge distortions of its own over time.

2. p=20% Less bad case. 

Whether because control measures prove effective and allow countries to move from mitigation back to containment (tracking & tracing all contacts, quarantine); warmer weather mitigates the virus’s propagation; a vaccine and/or therapeutics are announced that calm people down; etc; we begin recovering within 3 months.  Health care systems rapidly build capacity to keep fatality rates low.  While the virus persists, people accept that the risk for many individuals is not that much higher for most people than seasonal flu (for which many don’t choose to get vaccinated) or other normal but risky activities, and we live with some degree of behavioral changes (hand washing) and a degree of social distancing as a new normal.  Final attack rates (% of population infected) come in well below the 25-80% ranges widely discussed, and/or IFRs are below 0.5%.   In this scenario, we may have already seen the market bottom and despite a bad recession over two quarters, economies rapidly recover.  No long-term damage is done to the world’s productive capacity.

3. p=20% Worse case.  Like the expected case but worse.  It could be that control measures are unsustainable or ineffective and we see multiple waves of the epidemic; attack rates are more in the 50-80% range than the 25-40% range; IFRs are greater than 1%.  Perhaps there is mutation in the virus to become deadlier; or we see annual recurrence; or poor countries have extreme outbreaks and become long-term reservoirs of the virus.  Global tensions linked to COVID-19 drive geopolitical conflict, trade wars, currency wars; etc.  

Bill Gate’s AMA on Reddit

Speaking of arguments against the emerging “expected case”, Bill Gates participated in an “Ask Me Anything” session on Reddit yesterday, 19 March 2020.  I thought it was fascinating (thank you, William, for sharing it!) and excerpt several of the most interesting sections below.

Overall, you’ll see that Bill is more optimistic than Neil Ferguson (in fact, he directly attacks the Imperial College study) and thinks extreme control measures are only required temporarily.  That would be great news if true.

Besides the summary below, I also recommend checking out the Gate’s Foundation-funded Institute for Disease Modelling website, which has some highly curated resources and sources.  I was particularly interested in their summary of our best understanding of key parameters like R0, Serial Interval, CFR, etc.; and the sources of that understanding.

The format below is that all bullet points are direct quotes from BIll’s responses; they are preceded either by the exact question put to him, or grouped under a thematic heading.

  • Comments on Imperial College / Ferguson Paper:
    • Fortunately it appears the parameters used in that model were too negative. The experience in China is the most critical data we have. They did their “shut down” and were able to reduce the number of cases. They are testing widely so they see rebounds immediately and so far there have not been a lot. They avoided widespread infection. The Imperial model does not match this experience. Models are only as good as the assumptions put into them. People are working on models that match what we are seeing more closely and they will become a key tool. A group called Institute for Disease Modeling that I fund is one of the groups working with others on this.
    • (What about the NYTimes report that just came leaking a government document saying this will be 18 months with “multiple waves”?). There are many models to look at what will happen. That article is based on a set of assumptions derived from Influenza and it doesn’t match what has happened in China or even South Korea. So we need to be humble about what we know but it does appear that social distancing with testing can get the cases down to low levels.
    • The goal is to keep the number infected to a small percentage. In China less than .01% of the population was infected because of the measures they took. Most rich countries should be able to achieve a low level of infections. Some developing countries will not be able to do that.
  • Is there any chance that the 18 month timeline for development of a vaccine can be shortened, and by how much?
    • This is a great question. There are over 6 different efforts going on to make a vaccine. Some use a new approach called RNA which is unproven. We will have to build lots of manufacturing for the different approaches knowing that some of them will not work. We will need literally billions of vaccines to protect the world. Vaccines require testing to make sure they are safe and effective. Some vaccines like the flu don’t for the elderly.
    • The first vaccines we get will go to health care workers and critical workers. This could happen before 18 months if everything goes well but we and Fauci and others are being careful not to promise this when we are not sure. The work is going at full speed.
    • A therapeutic could be available well before a vaccine. Ideally this would reduce the number of people who need intensive care including respirators. The Foundation has organized a Therapeutics Accelerator to look at all the most promising ideas and bring all the capabilities of industry into play. So I am hopeful something will come out of this. It could be an anti-viral or antibodies or something else.
    • (Thoughts on chloroquine/hydroxychloroquine?). There are a lot of therapeutic drugs being examined. This is one of many but it is not proven. If it works we will need to make sure the finite supplies are held for the patients who need it most. We have a study going on to figure this out. We also have a screening effort to look at all the ideas for Therapeutics because the number being proposed is very large and only the most promising should be tried in patients. China was testing some things but now they have so few cases that that testing needs to move to other locations.
  • What do you think of the current approach the Netherlands is currently taking to combat this virus? They are not going to a full lockdown but rather try to spread it controllably in order to work towards ‘herd immunity’.
    • The only model that is known to work is a serious social distancing effort (“shut down”). If you don’t do this then the disease will spread to a high percentage of the population and your hospitals will be overloaded with cases. So this should be avoided despite the problems caused by the “shut down”. If a country doesn’t control its cases then other countries will prevent anyone going into or coming out of that country. I think the Netherlands will end up doing what other countries are doing.
    • The current phase has a lot of the cases in rich countries. With the right actions including the testing and social distancing (which I call “shut down”) within 2-3 months the rich countries should have avoided high levels of infection. I worry about all the economic damage but even worse will be how this will affect the developing countries who cannot do the social distancing the same way as rich countries and whose hospital capacity is much lower.
    • (What do you think about China’s approach?). After January 23 when they realized how serious it was they did strong social isolation which made a huge difference. Of course that isolation created a lot of difficulties for the people involved but they were able to stop the case spread. Other countries will do it somewhat differently but a combination of testing and social isolation clearly works and that is all we have until we get a vaccine.
  • How long will this go on?
    • This will vary a lot by country. China is seeing very few cases now because their testing and “shut down” was very effective. If a country does a good job with testing and “shut down” then within 6-10 weeks they should see very few cases and be able to open back up.
    • I think people in the US will be able to largely isolate for 2-3 months. If they can access testing including a home test kit then they will understand who is infected. I keep saying how important the testing piece is.
  • Won’t a rebound happen after the shutdown ends?
    • It depends on how you deal with people coming in from other countries and how strong the testing effort was. So far in China the amount of rebound being seen is very low. They are controlling people coming into the country very tightly. Hong Kong, Taiwan and Singapore have all done a good job on this. If we do it right the rebounds should be fairly small in numbers.
  • When will this all end?
    • To bring it to small numbers globally we need a vaccine. Many rich countries will be able to keep the number of cases small (including the US) if they do the right things but developing countries will find it very difficult to stop the spread so a vaccine is critical. A group called GAVI helps buy vaccines for developing countries and they will play a key role once we have a vaccine being made in volume.
  • Do you believe the news coming out of China though? It’s hard to at this point
    • China is doing a lot of testing. South Korea is also doing a good job of testing. Once China got serious in January they have been quite open about their cases so yes the good news is they are seeing very few infections at this point. The US needs to get its testing system organized so we see what is going on.
  • How is the economy likely to recover after all if this in your opinion
    • Yes eventually. The economic impact of the “shut down” will be large but if it is done well (including the testing piece which I keep mentioning) eventually we can open back up.
  • [I]t feels like our testing has not increased. Our number of confirmed cases are starting to lag behind other states. What do you think gives? Effective social distancing or lack of testing?
    • The testing in the US is not organized yet. In the next few weeks I hope the Government fixes this by having a website you can go to to find out about home testing and kiosks. Things are a bit confused on this right now. In Seattle the U of W is providing thousands of tests per day but no one is connected to a national tracking system.Whenever there is a positive test it should be seen to understand where the disease is and whether we need to strengthen the social distancing. South Korea did a great job on this including digital contact tracing.

Two other articulate points of view

Both of these are consistent with “expected case,” though neither is alarmist.  Michael Lin: “This is not the zombie apocalypse.”

The excellent Max Roser, consistently one of the most careful and precise thinkers on COVID-19, on “Many of you ask me why I take the COVID-19 outbreak so seriously.”

An MD/PhD’s very good slide deck on, “How to fight the coronavirus
SARS-CoV-2 and its disease, CoVID-19.”


3 thoughts on “Expected, better, and worse cases

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