Postscript and Post-Covid

September 29, 2020

by Sankar Das Sarma

This blog will primarily examine the absurd buzzword “post-covid”, which is often mentioned in a random manner in covid-19 discussions. I have no idea what it means or what people want to signify when they use this term. Post-covid is a true “unknown” unknown in the unforgettable jargon made famous by Donald Rumsfeld. It is not even a “known” unknown, so I do not know what people have in mind when they say “post-covid”.  We are in the middle of the covid-19 global pandemic with no logical or medical end in sight.  How does it make sense to talk about life post-covid?  What would “post-World War 2” have meant in 1940? Or what about “post-Great War” in 1914 or “post-Civil War” in 1861? 

But before I get to the meaninglessness of the term “post-covid”, I want to add a postscript to my last blog on herd immunity. There have been two recent developments since the publication of my last blog on September 21 concerning the idea of herd immunity which I believe necessitate a postscript.

The first one was a memorable exchange between Dr. Tony Fauci of the NIH and Senator Dr. Rand Paul of Kentucky concerning herd immunity during a senate hearing. You can view it here:

The second is a Twitter thread, based on a report in The Telegraph, that claims masks are somehow producing immunity to covid-19:

The exchange between Tony Fauci and Rand Paul is memorable not just because it reflects on Senator Paul’s dangerous obsession with eliminating all social distancing to control covid-19, ignoring common sense as well as overwhelming clinical evidence. It is memorable because Fauci finally lost his cool and could not take unadulterated nonsense from non-experts, even if the non-experts are sitting in positions of power. Fauci is of course careful about not losing his cool around the real source of power, sitting roughly a mile from the senate, who also promulgates covid-19 nonsense round the clock. Understandable as Fauci does not want to lose his job—that does no good whatsoever.

One thing about science that I believe is a good thing, it is certainly one of the main reasons I was attracted to science over literature or philosophy, is that truth matters. The truth cannot be negated by governments or the US Senate or the White House or even by a majority democratic vote. Scientific truth does not depend on the agreement from a majority of the people. If the whole world believes that the sun goes around the earth (as we once did) or the earth is flat (as we also once did), it does not matter because planetary orbits are scientific facts which cannot be decided by democratic elections.  The whole world may vote for a flat earth and only one person may claim the earth to be an almost round sphere, yet that single person still wins since the truth cannot be decided by votes.  Facts are just facts, independent of what people, even senators from Kentucky, believe.  For example, only about 30% of Americans apparently believe in evolution and 40% believe in creationism.  It does not affect anything since evolution is simply a scientific truth.  I can go on with more examples, but I think I made my point.

The senator made two inaccurate claims (that Fauci refuted compellingly): (1) Mask wearing is unnecessary against covid-19 and masks do not help and (2) the current situation in New York City and Sweden establish that many communities have now developed herd immunity.  In fact, the good senator simply has it backward here. It is the universal wearing of masks along with strict social distancing which has led to NYC being essentially ‘covid-free’ right now.  His claim that NYC, a place of 15 million people, is now somehow immune to SARS-COV2 is so incredibly wrong that it would be laughable if it was not so subversive and dangerous. The total covid-19 infection rate in NYC is of course unknown, but the best guess is that it is around 20%.  I have done enough simulations on this particular question to definitively state that no model provides a herd immunity for an infection rate less than 60%, no matter how unreasonably favorable one chooses the unknown parameters and boundary conditions to be.  Any reasonable model needs more than 80% (and reasonably long-lasting) immunity in the population for any type of viable covid-19 herd immunity.  

In addition, NYC has remained relatively covid free for months now (at least since mid-June) and any herd immunity would then require that the immunity lasts for 4 months for most people—a questionable premise for a coronavirus.  We do not get absolute immunity to the common cold for four months after catching a bad cold!  In fact, Senator Paul should have asserted that NYC proves that the use of masks, social distancing, “stay in place” orders, and lockdowns are essential in keeping covid-19 under control. Instead he somehow came to the opposite conclusion.  NYC, after suffering enormously in the early days of the pandemic, showed the rest of the country convincingly the only ways to fight covid-19 right now: lockdown, stay in place, social distancing, no crowds, and the use of masks. As for Sweden, well, I wish that Senator Paul (or at least someone in his senate staff) read my blog post of September 21—he would not then have made the incorrect comparison between Sweden and NYC to make his point. To claim that Sweden has done well with covid-19 by avoiding strict social distancing is false—it has done poorly compared with its neighboring nations, and is by far the worst affected Nordic country because of its reckless mistake of avoiding lockdowns.

As for mask-wearing leading to partial immunity, I am not so optimistic as this Telegraph article is.  The basic idea is not absurd, as Senator Paul’s claims are. The idea is that masks allow some limited exposure to SARS-COV2, which may just be enough (like a vaccine using a live virus) to create immunity.  I think that this is wishful thinking at this point, and any controlled experiments to establish this claim would be impossible, and possibly unethical. You have to first study control groups wearing masks and not wearing masks, and then reverse the situation (i.e. those wearing masks first go without masks and the ones who were not wearing masks start wearing masks), and each study must involve a lot of people and must go on for a long period of time to collect enough statistics to be able to say anything concrete.  I cannot claim that this is impossible—we simply do not know enough about our immunity to SARS-COV2 to claim that wearing masks cannot produce partial immunity.  But I am comfortable saying that it is by no means established at all that wearing masks gives one immunity to SARS-COV2, so you can stop wearing it at some point.  My guess would be that one’s chances for developing immunity based on just wearing a mask is likely to be much lower than that arising from an actual covid-19 infection.  We now know that one can be infected by SARS-COV 2 multiple times. So I strongly discourage anyone from discarding their masks because they believe that this has somehow made them immune to covid-19. Very unlikely in my opinion.

My final comment on the covid-19 herd immunity issue is the appearance of two recent reports, one by the CDC and one just published in Lancet, compellingly showing that only around 9% of the US population has developed antibodies to SARS-COV2 (how long the antibodies last on average is unknown) with the percentage varying from close to 25% in the NJ-NYC area to around 4% in the Western US. By any reckoning, perhaps even Senator Paul’s, any conceivable herd immunity which requires at least 80% of the population having antibodies is very far in the future. A linear extrapolation would suggest 5 more years. Trying to force it quickly by lifting all social distancing rules would likely kill 2 million more Americans, even if we make the simplest estimate. Of course, what matters are both the percentage of the population with immunity and the duration of the immunity in each individual. In addition, America is not a closed system, so any herd immunity must develop worldwide before we can get to “post-covid”. That is very far in the future, if ever.

Now onto my main topic: post-covid. 

I do not know what the term “post-covid” means nor where to begin. Obviously, there cannot be a single post-covid definition, there will be many different types of post-covid behavior depending on the specific aspects of life one is talking about. I can discuss post-covid behavior for going to crowded restaurants, going back to work, going to crowded basketball games, attending physics seminars, using public transportation, going to concerts, going to crowded classrooms, for taking long distance flights and so on. Each will have a different twist. It will also depend on the specific people and how they were affected by covid-19. Post-covid life for New York City will be very different from post-covid life for Wyoming, and post-covid life for a restaurant worker will be very different from post-covid life for a theoretical physicist. So, talking about a monolithic understanding of what it means to be post-covid is completely meaningless. 

For example, we can look at post-9/11 life in America. There has been no simple “post-9/11” in the sense of going back to exactly the same life as before 9/11. We all must go through serious security checks before boarding a flight, of course we got used to it, but those of us who flew extensively before 9/11 well remember the drastic (and permanent) changes 9/11 brought to commercial flying. For US soldiers who are (or were until very recently) posted in Afghanistan and Iraq for almost 20 years, there has not been a post-9/11.  For those who died in the wars arising from 9/11 there will never be a post-9/11.  What about countries like Afghanistan, Iraq, Syria, Pakistan, which are still suffering (and suffered enormously) directly as a result of 9/11?  There has been no post-9/11 for them even 20 years down the line.  Covid-19 is a much greater global crisis than 9/11 because this pandemic can potentially kill hundreds of millions globally, it has already killed a million, and has the capability to devastate the world economy far worse than the Great Depression of the 1930s. India’s economy has already shrank by 25% from the direct impact of the covid-19 pandemic and it continues to shrink, creating tremendous human misery. So, discussing post-covid is meaningless until we reach a stage where we have a much better control and understanding of the disease. That time is not now, and my guess is that such a time will not occur until long after effective vaccines have been introduced and proven to be successful against SARS-COV2. 

So, “post-covid” should be discussed no earlier than 2022, if even then, unless covid-19 disappears suddenly because of a particularly drastic mutation. After all, this could happen. But I do not recommend counting on it. One thing however is clear, there are likely to be some permanent behavior changes forced by covid-19 on human societies. What they might be is not so easy to guess right now, but possibilities are many:  A large fraction of people may decide to continue wearing masks; public crowded places may be regulated in some manner; countries may require covid-19 tests as a routine part of issuing visas; we may have to carry IDs showing that we have been vaccinated against covid-19 to enter any public place (e.g. restaurants, flights, concerts, stadiums, colleges and universities….).

Although “post-covid” in an absolute sense is very far in the future, partial “post-covid” life is happening around us every day in our mundane daily activities.  For example, I dine out regularly in Washington DC restaurants, at least three times a week, ever since the DC restaurants started reopening at 50% occupancy in late-June. I am careful in the sense that I keep my mask on except while eating and make sure that I sit far from people. I am still taking a small chance of course, but this is a choice I am willing to make because of my love for good food. I do not, however, fly or take Amtrak any longer. However my sons visit me from Chicago and NYC almost monthly flying commercially or on Amtrak. Again this is a choice they made while our pre-covid tradition would have been me visiting them, not their visiting me. I used to travel extensively during pre-covid life (around >100,000 miles of flying annually) but I have stopped traveling completely, and am unsure when I will be flying again. I work mostly from home because theoretical physics can be done from anywhere. There will not be a single post-covid set of behaviors, but there will be cascades of post-covid activities every day depending on the local situation and individual choice. The key point is that if “post-covid” defines the way we used to live in 2018 or 2017, well, I do not think that such pre-covid life is ever coming back. We all will have to take precautions constantly (e.g. wearing masks and avoiding crowds as much as possible) for the indefinite future.  I am sure that any post-covid life will differ qualitatively from the pre-covid one we remember.

To understand why the word post-covid is not a meaningful term, we must first understand why covid-19 is such a deadly pandemic. I pinpoint four specific reasons: (1) It is an extremely infectious respiratory disease which is carried through air; (2) humans have no immunity to it since SARS-COV2 is a completely new virus for humans which made its zoonosis to homo sapiens sometime late in 2019; (3) it causes serious illness, leading to pneumonia and other conditions, with a death rate averaging around 1%, which is exceptionally high given how infectious the disease is; (4) a large fraction of the infected people are asymptomatic, but nevertheless continue spreading the infection for weeks without realizing it. 

There are diseases which are probably more infectious (e.g. the common cold), but such ailments rarely lead to fatalities. There are infectious diseases (e.g. SARS, MERS) which have a higher fatality rate (almost 10%) but they happen to be much less infectious. So, covid-19 is unique in the sense that it has optimized both the infection efficiency and the fatality efficiency. If it was less infectious, but more fatal, it would be bad for only those unfortunates who catch it, but not such a huge public health problem.  If it was more infectious, but less fatal, well, we could live with being a little sick because we would not die. Covid-19 has maximized a 2-paramter function, and it affects EVERYBODY because EVERYBODY must breathe. It is an exceptionally easy disease to catch, simply by breathing the air near an already-infected person you can become infected. So, any concept of post-covid must involve suppression of the infectiousness as well as the suppression of the fatality rate. Although they obviously depend on each other, these two should be treated as constrained independent parameters since most infected people do not die, but there is no way to know who may die, so we must work on reducing both. 

The suppression of the fatality rate is likely to improve with time using various steroids or other drugs and using oxygen more effectively (without intubation, for example). But without the suppression of the infection itself, we cannot discuss any idea of post-covid life because our lives changed from pre-covid days only because we are collectively trying not to get infected by SARS-COV2 with lockdown, stay in place, social distancing, eliminating crowds, and wearing masks. So, any true post-covid will come after one (or more) of the following happens: (1) Herd immunity; (2) successful vaccines; or (3) the disappearance of SARS-COV2 in humans through mutations. There is no question that number three is our best option, but unfortunately we do not control it. As for items 1 and 2, I discussed in my last two blogs the challenges involved in both, and I do not see any light right now at the end of the proverbial tunnel. 

This is not the time to discuss the idea of life post-covid. Let us do it at the appropriate time when we have more scientific facts about SARS-COV2 and our immunity to it. The earliest time that I can even dream about doing so is the beginning of 2022.  Meanwhile, wear your mask, do as much social distancing as possible, avoid crowds obsessively, and simply hunker down (without paying any attention to all the nonsense involving herd immunity and effective vaccines in the pipeline).

Perhaps the readers want me to speculate about how covid-19 may play out in the future, if not about any post-covid scenarios. As a theoretical physicist, educated speculations are parts of my job description, so I will do so reluctantly.  Reluctance comes from knowing that important facts about covid-19 are unknown. How immunity develops, how long it lasts, how effective (or ineffective) any future vaccines are likely to be, what mutations are likely, if people will continue social distancing to keep the disease under control, and whether SARS-COV2 will become more or less deadly as it passes through humans extensively are all questions that one must consider when considering the future. Nevertheless I will speculate based on my understanding of the situation today and on the extensive modeling we have done on simple lattice models. Below is my best guess about the future.

The disease will continue basically as now for more than twelve months at least, certainly until the end of 2021, with multiple waves involving increasing/decreasing infections and fatalities in specific localities and countries as people decide to relax and then resume social distancing. These waves will be of many different amplitudes and periods depending on the locality, and the fatality rate of the infected people is likely to remain around 1% (perhaps going down slightly with better treatments and therapeutics). In the US, I do not see the fatality going far below 500-1000 per day for any extended time period, but it is unlikely that we will see again the exceptional mortality of 2000-3000 per day affecting New York City in the early days of covid-19. Worldwide the fatality will be some number around 4000-10000 per day, making it the third largest killer just below cancer and heart disease.  Eventually vaccines will start becoming available sometime in late 2021, but I simply do not see any vaccine having better than 50% effectiveness (and typically the average vaccine immunity will be at most an order of a couple of months).  It is ENTIRELY possible that in the future getting a covid-19 shot a month will become normal practice for everybody.  Eventually, I hope that some real immunity will develop when basically everybody has been exposed to SARS-COV2 repeatedly.  I do not know how long that will take since it depends on many factors.  I suspect that sometime in 2023 we may start seeing some real affects associated with herd immunity.  Perhaps starting in 2025, if we are lucky, covid-19 will become a chronic human disease similar to the flu, except much more deadly.  I would not be surprised at all if covid-19 remains the third largest killer of humans for the foreseeable future.  My fear is that it has the potential of becoming more dangerous, in principle, a far deadlier killer than the depressing future I describe here. 

I should add that my confidence level in my own predictions above is not high since it involves so many assumptions about unknown unknowns, but quite generally, I trust my predictions much more than all the completely baseless rosy predictions about covid-19 suddenly magically disappearing that we hear so much about.

To reinforce the point of the wavy nature of the pandemic, it is instructive to look at the covid-19 maps (see below) of several major countries (taken from NYT on September 26).  One can see that while the US (the first figure  below) is entering its ‘third wave’, India (fifth figure) and Brazil (sixth figure) are just ending their first waves whereas the European countries (Spain, the second figure; France, the third figure, and UK, the fourth figure) are getting into their second waves. There are countries, e.g. Belgium and Israel (neither shown here), where the third wave is already well under way. These waves will continue indefinitely with varying amplitudes and periods, depending on many known and unknown local factors until global immunity and/or effective vaccines (most likely a combination of the two) develop. I see no respite in less than two years, and I worry about the next huge tidal wave potentially coming to the US late this fall when conditions for spreading an infectious respiratory virus are ideal.

United States

United Kingdom


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

Create your website at
Get started
%d bloggers like this: