The Great Reconciliation?

What is the best way to reconcile the results for these three polls?

I’m tempted to just say “cognitive dissonance.”  The initial effort heuristic makes great sense, and the medical estimate seems about right.  But that in turn implies that past and current coronavirus efforts (public and private) are grossly excessive.  Indeed, do we even spend five hours per year fighting flu?  If so, why should we spend more than twenty five hours per year fighting coronavirus?  But almost no one feels comfortable with that relaxed attitude, hence the dissonance.


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The Risks of Friendship: A Socratic Dialogue

The scene: Ancient Athens.  Glaucon is standing in the Parthenon, wearing a face mask.  Socrates enters without a mask.

Socrates: Greetings, Glaucon!  How do you fare during this awful pandemic?

Glaucon: [jumps 5 feet]  What the hell are you doing?  Are you trying to kill me?

Socrates: No, why would you think so?

Glaucon: We’re indoors and you’re not wearing your mask!

Socrates: I’m 20 feet away from you.  And the Parthenon is cavernous.

Glaucon: You should be wearing a mask.

Socrates: Very well. [dons mask]  Feel safe enough to talk now?

Glaucon: [unconvincingly] Sure.

Socrates: I suggest we go outside to continue the conversation with greater ease.

[One minute later, outside the Parthenon; Socrates and Glaucon are 25 feet apart.]

Socrates: I must admit, Glaucon, I’m very puzzled.

Glaucon: About what?

Socrates: About your level of fear.

Glaucon: [with trepidation] Oh, I’m not afraid.

Socrates: Well, what do you think are the odds that I’ve got the plague right now?

Glaucon: Uh, one in a thousand?

Socrates: Reasonable enough; I’m asymptomatic after all.  Now, supposing I was sick, what are the odds that I would have infected you within the Parthenon while wearing a mask?

Glaucon: One in twenty?

Socrates: Plausibly.  And what are the odds I would have infected you in the same scenario without wearing a mask?

Glaucon: One in five?

Socrates: Very well.  Now as we both know, susceptibility to the plague depends heavily on age and underlying conditions.  We’re both fifty.  Do you have any underlying conditions?

Glaucon: Thankfully, no.

Socrates: Then according to a table Plato compiled for me, your odds of death if infected are about 1 in 2000.

Glaucon: It’s not just about the risk of death, Socrates!

Socrates: It never is.  There is also the unpleasantness of the plague’s symptoms, and a small chance of long-run harm.  Still, the same goes for almost all risks.  Those who survive a fall from a horse usually suffer pain for a week or two – and a small fraction are maimed for life.  So we can still fruitfully compare your risk of death from plague to other mortality risks, never losing sight of the fact that death is only one of many possible tragic outcomes.

Glaucon: [nervously] Fine.

Socrates: Very well, let us calculate the risk I imposed on you earlier by not wearing a mask.  We multiply my risk of infection times the change in your infection risk times your mortality risk.  That comes to 1/1000 * (.2-.05)* 1/2000, which rounds to about 1-in-13 million.

Glaucon: And that seems small to you.

Socrates: Wouldn’t it seem small to any sober man?

Glaucon: Well, is it really so awful to wear a mask?

Socrates: I wouldn’t mind if the numbers were more favorable.  If I were endangering a thousand people like you, I’d happily wear the mask.  As it stands, though, your fear seems paranoid and your outrage seems unjust.

Glaucon: Look, why should I have to endure any risk for your comfort?

Socrates: You’re enduring a risk right now.  Surely you don’t imagine that your infection risk magically falls to zero as soon as you exit the Parthenon?

Glaucon: Well, why should I have to endure an unnecessary risk?

Socrates: It is “necessary” that we speak at all?  Hardly.  And we could slash our risk further by separating a hundred feet and shouting at each other.

Glaucon: Now you’re just being difficult.

Socrates: I only wish to understand you, Glaucon.  Is that your horse over there?

Glaucon: Yes, Pegasus is his name.

Socrates: A noble moniker.  Now do you know the annual risk of dying on horseback?

Glaucon: About one in ten thousand?

Socrates: Indeed.  Yet you’ve never fretted over the risk of death by horse?

Glaucon: The daily risk is 365 times lower, or hadn’t you considered that?

Socrates: Quite right.  The daily risk of death by horse is therefore about 1-in-4 million – less than one-third of the risk that terrified you inside the Parthenon.

Glaucon: As long as I’m alone, I’m not exposed to any risk of plague at all.

Socrates: And as long as you’re unhorsed, you’re not exposed to any risk of death on horseback.  Yet during the minutes you’re on horseback, you’re a model of composure.  Why then are you so fearful of plague?

Glaucon: Plague is contagious.  Death on horseback is not.

Socrates: I’ve seen you riding with your son, slightly endangering his life as well as your own.  That’s not precisely “contagion,” but you can hardly claim that you’re endangering no one but yourself when you ride Pegasus.

Glaucon: If I catch plague, though, I could be responsible for the deaths of thousands.

Socrates: Possible, I’ll grant.  If I were returning home from a plague-infested land, I’d understand your scruples.  You wouldn’t want to be the conduit for mass destruction.

Glaucon: Indeed not.

Socrates: By now, however, this plague is already well-advanced.  You’re highly unlikely to make it noticeably worse.  Indeed, by this point the average person infects less than one extra person.

Glaucon: I might not be average.

Socrates: You are right to say so.  Still, shouldn’t our knowledge of averages guide our behavior?  In any case, let us return to the key issue: Why are you so fearful of talking inside the Parthenon without masks when the risk of death is vanishinly low?

Glaucon: Perhaps we should sponsor a raging Bacchanalia, then?

Socrates: I think not.  A drunken festival of a hundred people would probably have a thousand times the plague risk of a two-person conversation.  We should avoid that until the plague subsides.

Glaucon: So you admit the danger?

Socrates: I always did.  I’m not saying that plague is harmless.  I’m saying that you’re reacting to risk qualitatively rather than quantitatively.

Glaucon: Meaning?

Socrates: You’re much more afraid of a tiny plague risk than a larger horseback risk.  Why do you think that is?

Glaucon: Have you ever seen someone die of plague?

Socrates: Have you ever seen someone die on horseback?  Both are terrible tragedies, with a long list of ugly secondary risks.

Glaucon: Look, you’re in denial.  Everyone in Athens is scared of the plague.  Your risk analysis is beside the point.

Socrates: How can risk analysis ever be “beside the point”?

Glaucon: We as a society have decided to fight the plague, and you’re going to have to do your part, like it or not.

Socrates: Glaucon, what is my profession?

Glaucon: What?

Socrates: I said, “Glaucon, what is my profession?”

Glaucon: You’re a philosopher.

Socrates: Indeed.  As as a philosopher, what is my mission?

Glaucon: To defy and aggravate others?

Socrates: Hardly.  As a philosopher, my mission is to improve the thinking of my fellow Athenians, my fellow Greeks, my fellow human beings.

Glaucon: [sarcastically] Very noble.

Socrates: I take a certain pride in my efforts.  How, though, am I supposed to improve their thinking?

Glaucon: I don’t know.

Socrates: The answer, seemingly, is: By asking questions.

Glaucon: [weary] Yes, yes.

Socrates: Now Glaucon, when you urge me to “do my part,” what do you have in mind?

Glaucon: Wear the mask, Socrates.

Socrates: I’m wearing one now, to put you at ease while we converse.  In more crowded conditions, I’ve worn a mask out of prudence and decency.  But as a philosopher, obediently wearing a mask is woefully inadequate.

Glaucon: Well, what more should we do?

Socrates: I don’t know about non-philosophers.  For we philosophers to “do our part,” however, requires us to challenge popular fallacies and innumeracy.

Glaucon: Isn’t this just an elaborate rationalization for putting your own comfort above the lives of your fellow Athenians?

Socrates: Possibly.  More likely, though, your agitation is an elaborate rationalization for putting conformity above reason.

Glaucon: Your numbers could be wrong, you know.

Socrates: Indeed, I suspect that all of my numbers are wrong.  As we learn more, each of my numbers will be revised.

Glaucon: If you don’t really know the risks, why are you lecturing me?

Socrates: Because, Glaucon, you’re approaching the uncertainty emotionally rather than analytically.  Uncertainty is a poor argument for panic.

Glaucon: I was never “panicked.”

Socrates: Very well, let us take off these masks, enter the Parthenon, and continue the conversation in comfort.

Glaucon: Are you crazy, Socrates?

Socrates: And a corruptor of the youth, from what I hear.  Do you think there will be a trial?

Glaucon: Look who’s panicking now!

Socrates: A fair point, my dear Glaucon.  A fair point.

Glaucon: Look Socrates, it all comes down to this: There’s no reason not to just go along with society’s expectations here.

Socrates: No reason?  What about friendship?

Glaucon: I don’t follow you, Socrates.

Socrates: Since this plague struck, I’ve barely seen you.  Mask or no mask, you avoid me, as you avoid almost all human contact.

Glaucon: Well, what do you expect me to do?

Socrates: Weigh the tiny risks to health against the immense value of friendship.

Glaucon: You’re making too much of this, Socrates.

Socrates: Am I?  The great Epicurus taught us that friendship is one of the highest of goods.  Friendship is essential to human happiness, and a life well-lived.

Glaucon: You speak unjustly me to, Socrates.  I am and ever have been your friend.

Socrates: I know, which is why your panic pains me so.

Glaucon: If you’re really my friend, you will share my concern for my own safety.

Socrates: I do, Glaucon.  If you were in serious danger, and I could save you by shunning you, I would grieve.  Yet shun you I would.

Glaucon: Very gracious of you.

Socrates: I know you would do the same for me.

Glaucon: Again, most gracious.

Socrates: The plain fact, however, is that you are not in serious danger.  By the numbers, you are in the kind of minor danger that you’ve always accepted in the past.

Glaucon: And?

Socrates: And so I say the time is long since past to resume our normal friendly relations.  In troubles times, minor adjustments are often wise.  But abandoning your friends out of fear of minor risks is folly, Glaucon.

Glaucon: [forced] Well, thank you for your candor, Socrates.

Socrates: [resigned] May we meet again in saner times, my friend.

Glaucon: Good day to you, Socrates.  Good day.

[Glaucon and Socrates go their separate ways.]


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Sweden and Taiwan revisited

On April 15, I did a post arguing that Sweden is not the right Covid-19 model for libertarians, rather Taiwan is the model. Now that we are in September, it’s time to revisit some of the arguments.

One argument is that countries trying to control Covid-19 were merely delaying the inevitable. You hear people saying “we’re all going to get it eventually”.

But are we? Russia and China are already beginning to roll out vaccines, and Western countries are expected to begin doing so relatively soon. Back in mid-April, Taiwan had suffered 6 deaths in a population of 24 million—today its death toll is 7. Sweden has suffered 5813 deaths in a country of only 10 million. It’s not obvious to me that everyone in Taiwan will get Covid-19 before vaccines are available.

Sweden’s GDP has fallen by 7.7% over the past year, which is better than the European average but worse than the average performance of its Nordic neighbors (as I predicted). Taiwan’s GDP is only down about 0.1% over the past 12 months.  (Down 2.4% over the past 6 months, but even there it does much better than Sweden.) Thus while both countries refused to shut down schools and restaurants; Taiwan did far better in terms of both health outcomes and GDP growth.

The so-called “sophisticated” argument against my Taiwan/Sweden comparison focuses on structural differences between the two countries. And indeed there are many cultural, political and technological differences that do help to explain the differing outcomes. So (it’s claimed) perhaps there was no chance that the Swedes would undertake the Taiwanese approach in early 2020.  I agree.

But I’d actually call that a “pseudo-sophisticated” argument, as on close examination it’s not very helpful. I do have a deterministic view of how history plays out, so I don’t disagree with the claim that Sweden was unlikely to adopt the Taiwanese model in early 2020. But that misses the whole point of analysis and criticism. The point is not to rerun history—that cannot be done—rather the point is to learn lessons so that we are better prepared next time around.

Let’s suppose that in 10 years another dangerous virus emerges in China. I am confident that people will recall that the Taiwanese approach worked far better than the Swedish approach. Thus a key “pre-existing condition” that led to the Swedish failure in 2020 will no longer be operative. The public and politicians will understand that with an aggressive system of mask wearing plus test/trace/isolate it will be possible to prevent the disease from becoming widespread in any country with reasonable state capacity and civic virtue (which describes Sweden.) People will know that Taiwan was able to keep its schools and restaurants open, its economy running, and also avoid thousands of pointless deaths. That’s a powerful example.

Or at least they’ll understand that mask wearing plus test/trace/isolate work if I have any say in the matter, which is why I continue to post on this issue.


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Personal Immunity and Herd Immunity

When I first heard friends getting excited about T-cell immunity to COVID-19, I was non-plussed.

“This means the disease is less contagious than we thought!,” they said.

And I replied, “You’re double-counting!  I If some people are immune, that will already be reflected in existing estimates of R0.”

As it turns out, however, my friends were right for the wrong reason.  While immunity doesn’t matter for initial estimates of R0, it is crucial for estimating the path of R0.  This in turn is crucial for ascertaining when the pandemic will end.  David Friedman explains everything with admirable clarity:

Suppose, for simplicity, that half the population consists of people vulnerable to the disease and half, for behavioral or biological reasons, invulnerable. Observing the early spread of the disease, we find that, on average, each infected person passes the disease on to two others. We conclude that we will only reach herd immunity when half the population have had the disease and become immune as a result.

But the relevant figure is not what fraction of the population has become immune but what fraction of the vulnerable population has. In my simple model, half the vulnerable population is only a quarter of the total population, so we reach herd immunity much earlier than the simple calculation implies.

Semi-experts are often quick to say that you can’t reach herd immunity until 60-70% of the population gets infected.  If half of the population is immune, however, this is plainly wrong.  If 50% of the population is immunity, you’ll never hit 60-70% infection rates!

So what’s the correct story?  Consider the classic logistic contagion graph:

The key question is: Where’s the asymptote for the infected share of the population?  If everyone is vulnerable, you probably won’t hit the dashed line until most people get sick.  As the immune share of the population goes up up up, though, the dashed line shifts down down down.

The real question, then, is not whether individual immunity helps, but how much.  Many countries now look like they’ve hit herd immunity.  But as Scott Sumner emphasizes, “herd immunity with the help of drastic behavioral changes” is a far cry from “herd immunity with normal behavior.”

Unfortunately, both versions of herd immunity superficially look the same.  To tell them apart, you have to relax behavior and restrictions and see if the pandemic returns.  So while my improved understanding of the mathematics of immunity makes me more hopeful in the long-run, in the medium-run I remain diffident.  I won’t be surprised if the pandemic is over in every U.S. state by Christmas.  I won’t be surprised if the pandemic is worse in every U.S. state by Christmas.

Closing thought: The extreme rarity of public bets on the path of the pandemic tells me that even the best-informed experts remain about as confused as I am.  They’re just too high on their own putrid punditry to admit that they know little indeed about what’s going to happen.  I wish they would read Tetlock’s Superforecasting before they speak another negligent word, but I know they won’t.


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Covid-19 in the Western Hemisphere

Tyler Cowen recently made this claim:

That is the abstract of a new NBER paper by Andrew Atkeson, Karen Kopecky, and Tao Zha. You will note that when it comes to Covid-19 cases, the superior performance Europe had enjoyed over the United States seems to be evaporating.

I view case data as unreliable, especially when making international comparisons.  I prefer mortality data, which shows the US to be doing far worse than Europe, a gap that continues to widen dramatically:

In fairness, deaths lag infections by several weeks, so it’s possible that the US/Europe gap will soon begin to narrow.  My prediction, however, is that a month from now the gap will be much wider than today.  I further predict that when vaccines become available (probably in 2021) the gap will be still wider.  And I predict that studies will show that the gap reflects more than just different definitions of Covid-19 deaths, that excess death data will present a similar picture.

This graph is quite striking in that is shows that Covid-19 is currently a mostly Western Hemisphere problem.  The absolute number of deaths in countries like India is fairly large, but in per capita terms most of the deaths are occurring in the Western Hemisphere.

Western Hemisphere countries don’t have a lot in common.  The US is rich and Honduras is poor.  One thing these countries do have in common is high murder rates—by global standards.  Of course Canada is the exception.  But notice that Covid-19 deaths rates in Canada resemble Europe more than other Western Hemisphere countries.  Perhaps Canada should be viewed as a European country stuck in the Western Hemisphere.

PS.  Elsewhere I’ve argued that America increasing resembles what used to be called a ‘banana republic’.  Perhaps that term in no longer PC, but the phenomenon hasn’t gone away.


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Greg Ip Should Read the Wall Street Journal


In a lengthy article in today’s Wall Street Journal titled “New Thinking on Covid Lockdowns: They’re Overly Blunt and Costly,” Wall Street Journal reporter Greg Ip does a good job of backing up the title of his article. He shows that the title is justified.

Well, almost justified. The thinking isn’t exactly new. It’s been around for a few months, which makes it old in Covid-19 time.

In “The Data Are In: It’s Time for Major Reopening,” co-author Jonathan Lipow and I covered much of the reasoning that justifies the idea that lockdowns are overly blunt and costly in an op/ed. Where was the op/ed published?  In the Wall Street Journal, the publication that Greg Ip writes for. When? On June 16 (print) and June 15 (on-line.) The article is gated but you can read the whole thing here. That was 10 weeks ago.



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Philippe Lemoine on Covid-19 conspiracy theories

A great deal of confusing and contradictory information has been written about the events surrounding the outbreak of Covid-19 in Wuhan, China. Philippe Lemoine has now provided a long and carefully documented account of the early days of the epidemic. This will be followed up with three more installments, discussing conspiracy theories regarding acknowledgement of human-to-human transmission, the origin of Covid-19 (lab or natural), and pandemic data from China.

I approached this piece with a bit of skepticism, as in February I had been highly critical of China’s initial response and I had heard that Lemoine’s account was less critical of China. In fact, his account seems pretty even-handed and I found it persuasive. Here’s one excerpt, summarizing the events of late December 2019:

The truth is that, all things considered, and despite a few mistakes at the end of December, the identification of SARS-CoV-2 as the cause of the outbreak was remarkably fast. It could probably have been identified even faster had the cluster of pneumonia been noticed sooner. According to the New York Times, which relied on Chinese media reports and interviews with former officials, the system created after the SARS epidemic in 2002–04 to detect outbreaks of infectious diseases didn’t work properly. Every suspicious case was supposed to be immediately reported to the national health authorities in Beijing, who employ people trained to detect contagious outbreaks and take steps to suppress them before they spread. This system was created to prevent precisely the kind of political interference that had kept Beijing in the dark and delayed the response at the beginning of the first SARS outbreak in 2002. According to the Times, it didn’t work because the local health authorities insisted on controlling what was reported to Beijing instead of allowing doctors to report the information, as intended. That is why the national health authorities only realized there was a cluster of unusual pneumonia in Wuhan on December 30th, when rumours of SARS began to appear on social media. . . .

Needless to say, bureaucratic ineptitude is hardly unique to authoritarian countries in general, or to China in particular. It is a consequence of human frailty, and the conduct of many countries during this pandemic—including, and perhaps especially, some of the West’s democracies—offers countless examples of bureaucratic incompetence. We’ll probably never know exactly what went wrong in those very early days of the pandemic and who bears personal responsibility for China’s mistakes, because police states do not conduct public inquiries that risk undermining their own legitimacy and authority. We can speculate that, had everything worked exactly as it was supposed to, SARS-CoV-2 might have been identified as the cause of the pneumonia outbreak a few days, or perhaps a week, sooner. But we don’t live in a world without human error, we live in this one.

There are several lessons to be drawn from Lemoine’s research (my interpretation, not necessarily his):

1. My February post suggesting that China was the worst possible place for a Covid-19 epidemic to begin was clearly wrong.  They made mistakes, but no worse than one would expect in most countries.

2.  The US government response to the epidemic was at least as dishonest as the Chinese government response, and far more incompetent.

3.  US government claims of a Chinese Covid-19 conspiracy are false.

This issue is important, as the US government is currently using the alleged Chinese cover-up as one of the excuses for starting a cold war with China.  Recall that the Spanish-American War, the Vietnam War and the Iraq War we all based, in part, on false conspiracy theories peddled by the US government.

I eagerly await the next three installments in his series.  I expect Lemoine’s full account to eventually become the definitive history of the initial outbreak.  Read the whole thing.


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The Bloodbath:The Dropout, Episodes 5 and 6

Part 3 of a #ReadWithMe Series

Read the earlier posts here and here.

By 2016, Holmes and Balwani had broken up, and he was leaving the company. Carreyrou’s series of articles about Theranos’s unreliable technology had been published in the Wall Street Journal. And yet, many of Elizabeth’s early investors, like Tim Draper, still defended her unreservedly as someone who is “doing a great thing for humanity” and “changing healthcare as we know it.” Channing Robertson, her early supporter at Stanford, also remained a strong supporter, though the podcast notes that there may be pecuniary reasons for that, as Robertson was paid about $500,000 annually by Theranos.


In June, 2016, the deal with Walgreens fell apart and Walgreens sued for $140 million. The suit was settled, but more suits seemed to crop up every day. And regulators were now saying that Theranos’s technology was so unreliable it posed an “immediate risk” to patient health and safety. Theranos now came under investigation by the SEC.


The Dropout does an amazing job of highlighting the contrast between Holmes’s confident, in-control, and authoritative demeanor in interviews, with her answers in her deposition to the SEC, where she responded to their questions with “I don’t know” and “I don’t remember” more than 600 times. Again, the podcast lets us hear the shakiness of her answers as she tries to evade and avoid. 


There’s enormous satisfaction in this fifth episode of The Dropout. Finally, someone is asking the right questions, and not letting Holmes’s standard answers pass without scrutiny. Finally, we hear Holmes faced with her claims and with the pile of evidence against them. The podcast notes that it seems that for Holmes “There was no distance between aspiration and reality.” Because she wanted the machines to work, she claimed that they did.


It’s a good way to get charged with fraud by the SEC. And that’s exactly what happened. Balwani pled not guilty. Holmes settled. And then the Department of Justice brought criminal charges.


As of now, the trial of Elizabeth Holmes–who pled not guilty to these charges as well–is still pending. It has been rescheduled several times, and on August 12, 2020, the trial date was set for March 9, 2021.


The last half of episode 5 and most of episode 6 of The Dropout are dedicated to trying to humanize Holmes and Balwani. I found this fairly unpersuasive, though I do understand the need to present something like an unbiased account. But details of Balwani’s father’s early death, or Holmes’s struggles as a dedicated but completely unsuccessful high school track athlete seem like so much weak tea in response to the collapse of their claims and their misleading of the public and the medical community for years.


And at the end of The Dropout we are still left without answers to our most important questions. Was Theranos a failure or was it a fraud? Is Elizabeth Holmes an innovator and entrepreneur whose idea just didn’t pan out, or is she a con artist? And how can we ever really know?

Her upcoming court case may give us some answers, but given the many difficulties of establishing intent to defraud in the ever-churning world of startups, I don’t hold out much hope for a definitive answer.


One more iteration of the story of what happened at Theranos, however, did give me a few answers to some other questions I had. Stay tuned for a final, quick post on Tyler Shultz’s podcast, Thicker Than Water.



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The Dysfunctional FDA


A front-page article in Wednesday’s print edition of the Wall Street Journal is titled “Three Lost Weeks Stalled Virus Testing.” (The title in the linked e-version is slightly different.) The reporters are Stephanie Armour, Brianna Abbott, Thomas M. Burton, and Betsy McKay. The investigative report is quite good.

It talks about a number of mistakes made up front by the CDC. But here’s a whopper about the FDA:

Complicating matters for commercial and hospital labs, a public-health emergency Mr. Azar declared Jan. 31 created a new regulatory hurdle: They would soon have to seek emergency-use authorization from the FDA, a potentially time-consuming process, before their tests could be used. In a nonemergency, hospital and academic labs are typically allowed to design and implement their own in-house tests without much regulatory oversight. The FDA spokeswoman said that, in many cases, the FDA can do this review in as little as a day.

Get that? If there’s not an emergency, commercial and hospital labs are allowed to use their own tests. But if there is an emergency, these labs must seek and get FDA authorization.

I do not think that word “emergency” means what the FDA thinks it means.


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Herd immunity is not a number (part 2)


COVID-19 researchers and modelers have assumed that at least 60 percent of a population, perhaps 70 percent, would need to be infected with the new coronavirus or vaccinated against it before reaching herd immunity, the point at which the virus can no longer spread widely among a community. Some infectious disease experts are now examining the “hopeful possibility” that far fewer people have to get infected or immunized to achieve herd immunity, The New York Times reports, citing interviews with more than a dozen scientists.

If their new, complicated statistical models are correct, and communities can reach herd immunity with 50 percent or less of people gaining immunity to COVID-19, “it may be possible to turn back the coronavirus more quickly than once thought,” the Times reports. A clear minority of researchers predict as few as 10 or 20 percent of a population developing antibodies to the disease would be sufficient for herd immunity; Stockholm University mathematician Tom Britton calculated the threshold at 43 percent.

I continue to see these extremely misleading articles, which suggest that herd immunity is some sort of stable parameter than can be estimated by scientists.  Actually, herd immunity is a function of behavior.

When Covid-19 first appeared it was highly infectious.  That led to estimates of 60% or 70% for herd immunity.  But unlike with the common cold, societies almost everywhere took precautions to reduce the spread of Covid-19.  Even in Sweden there was a great deal of social distancing.  Since April, social distancing in New York State has reduced the fatality rate from Covid-19 from almost 1000/day to near zero.  And that’s with antibody levels far below 60% (probably closer to 20%)


But if New Yorkers were suddenly to go back to life as usual, Covid-19 cases would likely rise sharply, as New York’s current situation of near herd immunity is predicated on a high level of social distancing and mask wearing.

This does not mean the initial 60% to 70% estimates are correct, even for a population taking no precautions.  Scientists now have a better understanding of issues such as natural immunity and heterogeneity in behavior (super-spreaders).  So the initial estimates may be incorrect.

Here’s how I look at things.  The US has a fatality rate of 533/million, rising fast.  Sweden’s has leveled off at 584/million.  But New Jersey’s at 1805/million deaths despite lots of social distancing.  Indeed I know people in New Jersey who work at home and are extremely unlikely to contract Covid-19 unless they go back to business as usual.  Thus even New Jersey is far from herd immunity with no precautions.  Therefore it’s unlikely that herd immunity was a sensible solution for the US back in April.  The entire US would have likely been hit even harder than New Jersey was hit.  (And recall that even official death rates probably undercount the true death toll, at least according to “excess deaths” studies.)

On the other hand, the fatality rates I cite for New Jersey reflect the medical care back in April, when most of the deaths occurred.  There is evidence that the death rate for Covid-19 (per actual case) has already fallen sharply in recent months.  With improved treatments, it’s very possible that at some point herd immunity will become the optimal strategy.  I’m agnostic on that question.  But it’s important to think clearly about these issues, and a number of recent news articles have done a disservice to the public by oversimplifying the problem.

PS.  People often focus too much on the public policy aspects of this issue.  When I said, “Therefore it’s unlikely that herd immunity was a sensible solution for the US back in April” I was not referring to public policy.  There’s no way the US government could have adopted herd immunity as a strategy, as the public would have done social distancing on their own, and indeed started doing so even before lockdown were in place.

It’s also worth noting that while Sweden’s economy did better than the Eurozone (so far); its recession was as bad as in Denmark and worse than in Finland. (Norway’s Q2 GDP data is not in yet.)  Sweden shows that substantial social distancing was inevitable.


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