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At the moment, basically every country seems to be busy avoiding catastrophe by a lock down. There is only little to no long-term exit strategy and for good reasons. However, the ultimate goal of achieving herd immunity is not achieved by a lock down. not publishing an exit plan does not mean that there are no plausible long-term scenarios. What are those?

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    I'm somewhat unhappy with this question-answer because it was apparently written to promote a specific Medium article, proposing a specific "hammer and dance" paradigm, which isn't even analyzed very scientifically in the original source. To adapt a certain phrase "beware of the [self-posted] answer based a single [popsci] article about [solutions to] Covid-19". – Fizz Apr 13 at 5:12
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    And yeah, one can obviously post other answers when the question is reopened (which looks like it's going to happen), but frankly the question is pretty broad. And how would one decide which answers are good to a question like this, i.e. "what options to they have"? It seems to me (self-answer aside) the question is inviting a popularity contest of proposed solutions to Covid-19. (See for example Johnathan's answer and the downvotes it has. The answer is technically on-topic, for some meaning of "option on the table", but sure it was DV because users here disagree with those proposal(s).) – Fizz Apr 13 at 5:22
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    The phrase "plausible long-term scenarios" is much more general than "long-term options ... politicians have". The latter usage suggests the possibility that long-term careerist politicians might avoid some sound public remedy that might endanger their personal long-term career -- as with a pol callously rejecting a better public health option in favor of any mediocre option that best rewarded their favorite lobbyist. Please clarify. – agc Apr 13 at 6:58
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    Actually, I found the medium article only while researching for English sources. But do with this question what you want. I already see that this obviously did not hit the personal agenda of some people and I am a bit disappointed that discussion about the question only started after people started to vote to reopen. – Manziel Apr 13 at 8:31
  • (-1) This question is a hot mess. After declaring (in your answer to the other question) that we know nothing and there could be no plan (which is plainly not true), you realize it is in fact possible but want to engage in armchair speculation based on a single article you happened to like. Obviously, not publishing a (new) plan doesn't mean there is no strategy either. – Relaxed Apr 14 at 13:20
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In general, a pandemic will only stop for good once a large part of the population is immune and infections can no longer spread freely. At the moment most experts assume that after an infection, the patient will be immune against Covid-19 for up to several years although there seem to be cases of reinfections in South Korea. It is not yet clear if these cases are related to errors during testing or actual reinfections.

With herd-immunity as the end goal, this leaves the following scenarios:

Complete elimination of the virus in a region/country
Through rigorous testing and a huge streak of luck the last infected person in a region is quarantined and the disease is effectively removed. However, it is still spreading in the outside word. Any contact with the outside world is now a dangerous endeavour and might import the virus again. Any visitor would probably be quarantined for 2 weeks on arrival. This approach only seems practical for regions that are already naturally isolated. The region must not depend on tourism in any way as the quarantine regulations will effectively kill tourism.

Uncontrolled Spread
A country does not want to take measures or is unable to contain the spread in any meaningful way. This is the most likely scenario for countries with a large population on income level 1 and 2 as a lock down and social distancing are nearly impossible to enforce in those countries. These will experience a fast spread of the infection, the health system will be overstressed and patients with serious symptoms are very likely to die. The only upside for these countries is that their population is very young on average and young people seem to show less serious symptoms.
An uncontrolled spread will lead to a natural herd immunity in a relatively short time (as compared to other scenarios).

Semi-controlled spread A semi-controlled spread involves closing of bigger events and groups of people, as well as the attempt to separate high-risk groups from the general population. This restricts everyday life for the high-risk groups a lot and for other people a bit. Low-risk groups could still go to the gym, the restaurant, etc. This approach has two main appeals. First, it places the main burden of restrictions on the groups that profit most from them (the high-risk groups) and a faster spread through the low-risk groups will gain immunity over time.
This is effectively the Swedish approach. This approach used to be favoured by Britain but was abandoned probably due to the high risk associated with it. As the infections spreads relatively fast it is very hard to monitor and control the spread. As long as only the low-risk groups are infected, the health system should be able to handle the stress but it can easily get out of control, for example if the virus finds a way into retirement homes.
A country that implements this approach probably will be treated as a high-risk zone by its neighbours implementing a more restrictive approach. After a medium time frame, natural herd immunity would be reached.

Slow + controlled spread within the systems limits ("flatten the curve") Flatten the curve
(Source: Wikipedia)
At the moment this approach seems to be everybody's favorite. Through a strict lock-down the curve is flattened to keep the number of infected patients within the health systems limits. The lock-down has a high impact on daily life, basically everything that involves meeting other people for fun is forbidden. All "risky" or injury prone recreational activities are also strongly discourage or forbidden even if they do not involve other people to preserve the healthcare system's capacity from motorcycle crash victims, etc. This causes an enormous economic and social damage as we can see right now. The problem is, the damage will not be for a short time but for a very long time.
ICU beds depending on R value
The figure shows a projection of the number of ICU beds needed in Germany taken from this article. To fit it into the capacities of the Germany health system with its relatively high number of ICU beds the spread needs to be R < 1.1 which means the the epidemic takes for years. In the projection, after 300 days the peak is not even reached. Herd immunity with this approach takes years. At the moment even the worst affected countries like Spain are at official infection rates way below 1%. Even for a large number of unreported cases, it is abundantly clear that this is still a far way from any meaningful herd-immunity.
It is unimaginable that any country can keep a sufficient lock-down until herd-immunity is reached. While there seems to be no major quarantine fatigue right now this is sure to come if people continue to be locked into their homes with nothing interesting to do, the economy breaks down and people lose their jobs. A prolonged hard lock-down also hardly fits into the concept of a liberal democracy

Contain and wait for vaccination ("Hammer and dance")
This begins with a hard suppression phase (the hammer) and is followed by a dancing phase that tries to lift restriction if possible and reintroduce them in necessary (the dance), keeping the spread low until a working vaccine is found. Testing and tracing of infection chains is one key component to keep the spread low. This is basically the strategy implemented by China. Hammer and dance
The figure is taken from an excellent article on how this is supposed to work with a lot of background on the concept.
The concept has the appeal that restrictions will (mostly) have an end and relatively normal life can resume at some point. It reduces the damage taken without taking millions of deaths (which would have their own price as well). It would allow travel to neighbouring countries that implement the same strategy and might even cooperate on tracing.
This approach however has two major drawbacks. First, it solely relies on the assumption that a safe and working vaccine can be found in a reasonable amount of time. This also assumes that the virus will not mutate in a way that multiple vaccines would be needed. Second, this requires to reduce the number of cases sufficiently to allow for testing and tracing. It is not clear how low this number needs to be but it requires substantial effort to reduce the number enough. This strategy also may fail, for example Singapore was employing the dance part relatively successful but is now on lock down as well

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  • SARS was also an epidemic ncbi.nlm.nih.gov/pmc/articles/PMC2636331 So there are exception to your rule "will only stop for good once a large part of the population is immune". The time/window for the SARS solution has probably passed though wrt. Covid-19. It's not clear how often Covid-19 can reinfect though... i.e. how persistent antibodies to it will be. See medicalsciences.stackexchange.com/questions/23174/… for a summary table of other viruses. – Fizz Apr 12 at 18:13
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    Yes, SARS was an epidemic but not on pandemic level. I fixed the introduction. And as far as I know it was basically eliminated world-wide (from humans). This is definitely not going to happen with Covid-19 – Manziel Apr 12 at 18:18
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    Also the extremely long-winded Medium article comes down to something much simpler that was better said by other [economists] e.g. Ornelas, i.e. there's probably an optimum of lockdown measures that varies with how spread the pandemic is, i.e. with "R0" [actually Rt] (Also the Medium graph is terrible.) For more complex models see Eichenbaum cited by Ornelas. (Eichenbaum's paper was also covered in a NYT article, if you search.) – Fizz Apr 12 at 18:28
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    It is not necessary to test everyone. This why the hammer is taken with a lock-down. You drive down the infections and at the end you only have to trace 5-10k people instead of 100k+. This is a whole different magnitude than starting wide-spread testing right-now. And the semi-controlled spread was basically abandoned by everyone except Sweden and the Netherlands. The risk of it getting out of control is really high and once it happen you only made the lock-down much much worse. – Manziel Apr 12 at 19:16
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    Technically China would indeed fall into the eradication category (assuming numbers are true). However, China probably does not want to isolate forever (bad for business) and therefore I placed them in the dance phase waiting for vaccination. – Manziel Apr 12 at 21:48
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In my opinion the best long term option is either a treatment of the virus or its symptoms. Any prophylactic like a vaccine may never eventuate during this pandemic. There are a lot of candidate antiviral drugs being tested, also a stem cell anti inflammatory (symptoms) from Mesoblast

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A few scenarios

These are reasons that politicians would likely use justify a lifting of restrictions. Picking one (or more) will be a political choice made by leaders. I posit that the list is in increasing order of political risk.

  1. Vaccine becomes widely available
  2. Effective and proven treatments become widely available
  3. Antibody tests allow asymptomatic cases to return to work
  4. Cases drop to rates sustainable by medical facilities
  5. Model projections show a much decreased public risk
  6. The economic ill-effects on health overshadows the virus
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I am going to go with Manziel's but with one big caveat:

Singapore and China have both implemented quite invasive surveillance technology, combined with limits on personal liberties, to get to this tighten-relax-tighten phase.

Right now, we are not discussing this much.

Here's a youtube video giving you an idea of China does.

Possible approaches are:

  • already-immune certificates indicating that someone already has had covid. Either by tracking who tested positive and got released. Or by antibody tests. Great idea, except that in practice, it would require you having to divulge your personal medical information.

  • pervasive tracking via apps on smartphones (not sure how that would work with people who don't have them), indicating risk levels

  • frequent mandatory checkpoint challenges based on things like temperature checks.

  • tracking temperatures at scale. For example, China lists temperature readings of anyone who prepped your food and workplaces are obligated to check employees' temperature readings. 2+ employees with a fever: call in health dept.

  • any other measure that has credible epidemiological effect but impacts personal privacy and liberty.

I am not sure if/when this type of measures is going to be discussed, but given that covid seems to be fairly highly contagious w a strong possibility of asymptomatic contagiousness, I am equally unsure how we would avoid a replay of something like the Lombardy area patient zero restarting the whole cycle all over again in an area that had relaxed, at least until we had vaccines and/or a really effective antiviral available.

i.e. quarantine 3 weeks, loosen up x weeks, quarantine 3 weeks, ... Each time, presumably, with the national government partially picking up the tab for people out of work and businesses at risk.

Now, don't shoot the messenger. I could be wrong and somehow we will find a way to enable large scale loosening of restrictions and not re-trigger local epidemics, without invading privacy and liberty. By large scale loosening, I mean things essentially going back to normal, with people doing their normal day to day jobs, with the exception of mass events like concerts, discotheques and trade conferences, etc... And NYC-type subways too. i.e. social distancing, but mostly open businesses.

But stating that there's a China model, without considering the lengths to which China has coerced its citizens to get there is missing a good deal of the picture. Whether we want to go there or not is another question, but let's at least be aware of what they've done when citing them as a model.

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  • "already-immune certificates indicating" ... presumably a certificate a person could voluntarily apply for. I'm anticipating the time (soon) when I can go to my favorite restaurant and not have to worry about the staff or fellow diners being unknowingly contagious. Frankly, I'd be much more comfortable going to a restaurant where the proprietor would insist on a "already-immune certificate" from his staff and his patrons. – BobE Apr 14 at 2:43
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There are two concepts currently emerging in the public discourse in addition to the list of solutions written down by @Manziel above.

Variolation

We know from empirical evidence that young doctors frequently succumb to the disease, most famously Li Wenliang - the original Chinese whistleblower who was merely 33 years old. The most common explanation for that phenomenon is that doctors are exposed to a high viral load from multiple patients which significantly increases their odds of death. This of course brings about an interesting question about the inverse - could we reduce the odds of death by purposefully infecting people with a tiny dose of the virus? This is where variolation steps in and proposes that we solve the COVID-19 crisis similarly to how we originally fought the smallpox epidemic.

As of this time no research laboratories are attempting to test this theory, but hopefully some will in the near future.

Herd immunity might be closer than we think

The last major worldwide pandemic was the 1918 flu, which is estimated to have infected 1/3 of the world population. But here you might ask yourself... why didn't it infect at least 2/3 of the population as predicted by current herd immunity theories? The answer might be that the current simplified models of herd immunity are too simplistic, as they assume that humans move around like bacteria in a Petri dish - randomly interacting with each other at all times. But of course human behaviour is more complex, as explained perfectly in this blog post:

One thing both economists and epidemiologists seem to be lacking is an awareness for the problems of aggregation. Most models in both fields see the population as one homogenous mass of individuals. But sometimes, individual variation makes a difference in the aggregate, even if the average is the same.

In the case of pandemics, it makes a big difference how that infection rate varies in the population. Most models assume that it is the same for everyone. But in reality, human interactions are not evenly distributed. Some people shake hands all day, while others spend their days mostly alone in front of a screen. This uneven distribution has an interesting effect: those who spread virus the most are also the most likely to get it. This means that the infection rate looks very higher in the beginning of a pandemic, but sinks once the super spreaders has the disease and got immunity. Also, it means herd immunity is reached much earlier: not after 70% of the population is immune, but after people who are involved in 70% of all human interactions are immune. At average, this is the same. But in practice, it can make a big difference.

I did a small simulation on this and came to the conclusion that with recursively applied Pareto-distribution where 1/3 of all people are responsible for 2/3 of all human interaction, herd immunity is already reached when 10% of the population had the virus. So individual variation in the infection rate can make an enormous difference that are be captured in aggregate models.

If this analysis is correct and we can achieve herd immunity at 10% infection rates, we might be able to go back to normal a lot faster than predicted, even without a vaccine being in place.

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  • @Fizz there are many possible variations, but they all come down to the idea that a controlled infections is a lot safer than a random one. Just how safer and which technique is the best can only be learned empirically. – JonathanReez Apr 13 at 6:00
  • Sorry if I'm late to the party. "If ... we can achieve herd immunity at 10% infection rates,we might be able to go back to normal" ... How are you calculating infection rate? Also, what is the threshold for herd immunity? - Some have suggested that ~90% or greater of the population would have to be immune to stop the spread. – BobE Apr 14 at 4:08
  • @BobE 90% presumes we all interact with each other equally like bacteria in a Petri dish. But some of us meet more people than others, which is why celebrities were more likely to get the virus at first. So once those who are most likely to spread the virus around are infected, transmission will slow down and the virus could become extinct. – JonathanReez Apr 14 at 4:11
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    How are you calculating infection rate? – BobE Apr 14 at 11:41

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