Why herd immunity is worth less than you might think

That is the topic of my latest Bloomberg column.  The evidence in favor of at least partial herd immunity continues to pile up, but still don’t get too cheery.  One worry is that herd immunity might prove only temporary:

First, many herd immunity hypotheses invoke the idea of “superspreaders” — that a relatively small number of people account for a disproportionate amount of the contagion. Perhaps it is the bartenders, church choir singers and bus drivers who spread the virus to so many others early on in the pandemic. Now that those groups have been exposed to a high degree and have acquired immunity, it might be much harder to distribute the virus.

That logic makes some sense except for one issue: namely, that the identities of potential superspreaders can change over time. For instance, perhaps choir singers were superspreaders earlier in the winter, but with most choral singing shut down, maybe TSA security guards are the new superspreaders. After all, air travel has been rising steadily. Or the onset of winter and colder weather might make waiters a new set of superspreaders, as more people dine inside.

In other words, herd immunity might be a temporary state of affairs. The very economic and social changes brought by the virus may induce a rotation of potential superspreaders, thereby undoing some of the acquired protection.

In other words, the fight never quite ends.  Here is another and possibly larger worry:

Another problem is global in nature and could prove very severe indeed. One possible motivation for the herd immunity hypothesis is that a significant chunk of the population already had been exposed to related coronaviruses, thereby giving it partial immunity to Covid-19. In essence, that “reservoir” of protected individuals has helped to slow or stop the spread of the virus sooner than might have been expected.

There is a catch, however. If true, that hypothesis means that the virus spreads all the more rapidly among groups with little or no protection. (Technically, if R = 2.5, but say 50% of the core population has protection, there is an R of something like 5 for the unprotected population, to get the aggregate R to 2.5.) So if some parts of the world enjoy less protection from cross-immunities, Covid-19 is likely to ravage them all the more — and very rapidly at that.

Again, this is all in the realm of the hypothetical. But that scenario might help explain the severe Covid-19 toll in much of Latin America, and possibly in India and South Africa. Herd immunity, as a general concept, could mean a more dangerous virus for some areas and population subgroups.

There are further arguments at the link.

The classical theory of economic growth, by Donald J. Harris

By Donald J. Harris, here is the abstract:

Focused on the emerging conditions of industrial capitalism in Britain in their own time, the classical economists were able to provide an account of the broad forces that influence economic growth and of the mechanisms underlying the growth process. Accumulation and productive investment of a part of the social surplus in the form of profits were seen as the main driving force. Hence, changes in the rate of profit were a decisive reference point for analysis of the long-term evolution of the economy. As worked out most coherently by Ricardo, the analysis indicated that in a closed economy there is an inevitable tendency for the rate of profit to fall. In this article, the essential features of the classical analysis of the accumulation process are presented and formalized in terms of a simple model.

Here is the full piece.  Here are other pieces by Donald J. Harris, professor emeritus at Stanford, economist, and father of Kamala Harris.  Here is further background on him.

The film culture that is royal Britain

There have been few insights into what the Queen’s favourite film is but one might assume that it would be a black and white classic from her youth or perhaps Black Beauty.

According to Brian Blessed, however, one of her favourite films is Flash Gordon, the 1980 high camp space opera in which the actor stars as Prince Vultan.

Blessed said that the Queen told him that she sits down to watch the science fiction film every year at Christmas with her grandchildren. The actor, 83, quoted the Queen as saying: “You know, we watch Flash Gordon all the time.” Blessed added that the Queen had then requested him to perform his catchphrase from the film.

“And if you don’t mind,” Blessed recalled the Queen saying, “I’ve got the grandchildren here, would you mind saying, ‘Gordon’s alive?’”

Perhaps, then, if Blessed’s claim is true, it is little surprise that her other viewing choices are more sedate. Royal sources have previously said that the Queen likes to watch the quiz show Pointless and The Bill.

You may recall that the soundtrack to the film was written by Queen, though not by “the Queen.”  Or perhaps she is simply a fan of Max von Sydow.

Here is the full (Times of London, gated) article.

Which time lags matter for testing regimes?

What determines the success of a COVID-19 Test & Trace policy? We use an SEIR agent-based model on a graph, with realistic epidemiological parameters. Simulating variations in certain parameters of Testing & Tracing, we find that important determinants of successful containment are: (i) the time from symptom onset until a patient is self-isolated and tested, and (ii) the share of contacts of a positive patient who are successfully traced. Comparatively less important is (iii) the time of test analysis and contact tracing. When the share of contacts successfully traced is higher, the Test & Trace Time rises somewhat in importance. These results are robust to a wide range of values for how infectious presymptomatic patients are, to the amount of asymptomatic patients, to the network degree distribution and to base epidemic growth rate. We also provide mathematical arguments for why these simulation results hold in more general settings. Since real world Test & Trace systems and policies could affect all three parameters, Symptom Onset to Test Time should be considered, alongside test turnaround time and contact tracing coverage, as a key determinant of Test & Trace success.

That is from a new paper by Ofir Reich.

The U.S. selects better for Asian immigrants than does Australia

Whereas Australia has pursued a skills-based migration policy, the United States has privileged family-based migration. The key contrast between these migration regimes provides a rare test of how national immigration policy shapes immigrant selection and integration. Does a skills-based immigration regime result in a more select group of Asian immigrants in Australia compared to their counterparts in the United States? Are Asian immigrants more integrated into their host society in Australia compared to the United States? Focusing on four groups of Asian immigrants in both countries (Chinese, Indians, Filipinos, and Vietnamese), this article addresses these questions using a transpacific comparison. Despite Australia’s skills-based immigration policy, we find that Asian immigrants in Australia are less hyper-selected than their counterparts in the United States. Asian immigrants in Australia also report worse labor market outcomes than those in the United States, with the exception of Vietnamese—a refugee group. Altogether, these findings challenge the conventional wisdom that skills-based immigration policy not only results in more selected immigrants, but also positively influences their integration into the host society.

That is from a new piece by Van C. Tran, Fei Guo, and Tiffany J. Huang, via the excellent Kevin Lewis.  The mix of offering a large potential market, and not so much welfare, is a significant part of the U.S. immigrant selection mechanism.

Coming soon, to a country near you

But let’s start with the UK:

The number of people in hospital with Covid-19 has fallen 96% since the peak of the pandemic, official data reveals.

Hospital staff are now treating just 700 coronavirus patients a day in England, compared to about 17,000 a day during the middle of April, according to NHS England.

Last week, some hospitals did not have a single coronavirus patient on their wards, with one top doctor suggesting that Britain is “almost reaching herd immunity”.

In a further sign of good news, the virus death toll in hospitals has also plummeted. On April 10, the day the highest number of deaths was announced to the nation, NHS England said 866 people had died. On Thursday last week, there were just five hospital deaths across the entire country. It represents a fall of more than 99% from the height of fatalities during the crisis.

Note that the pubs and many other venues have been open for over a month, and social distancing protections in the UK remain relatively weak, nor has individual or political behavior in the country been especially responsible.

Here is the Times of London piece (gated).

Monday assorted links

1. How safe is it to fly? (Bloomberg)

2. What is the share of the population with preexisting immunity?  Recommended.

3. And excellent David Wallace-Wells piece on the spread of herd immunity ideas and T-cell immunity (as more significant than had been thought) throughout the scientific community.  Also recommended.

4. Obesity and corruption.

5. Male earnings in the U.S. do not show a general volatility increase over the last 30 years.

The Contemporary Impact of Black G.I.s in Europe in WWII

Abstract: Can attitudes towards minorities, an important cultural trait, be changed? We show that the presence of African American soldiers in the U.K. during World War II reduced anti-minority prejudice, a result of the positive interactions which took place between soldiers and the local population. The change has been persistent: in locations in which more African American soldiers were posted there are fewer members of and voters for the U.K.’s leading far-right party, less implicit bias against blacks and fewer individuals professing racial prejudice, all measured around 2010. Our results point towards intergenerational transmission from parents to children as the most likely explanation.

from a new paper by David Schindler and Mark Westcott in ReStud. Black GI’s also experienced a society with much less segregation than in the United States.

Mixed race couples dancing in a London club, 1943. Original Publication: Picture Post – 1486 – Inside London’s Coloured Clubs – pub. 1943 (Photo by Felix Man/Picture Post/Getty Images)

Mixed race couples dancing in a London club, 1943. Original Publication: Picture Post – 1486 – Inside London’s Coloured Clubs – pub. 1943 (Photo by Felix Man/Picture Post/Getty Images)

From this review.

Rapid Tests

Here’s a good picture illustrating the difference between the PCR and Rapid Test. A PCR amplifies DNA and so if taken at the right time it will detect the virus before a rapid test will. But this happens when there isn’t much viral load and too little of the virus to be transmissible. Moreover, at these times, the virus is increasing rapidly so the rapid test will find the virus tomorrow. The PCR test will also pick up fragments after transmissiblity has passed which also isn’t very useful. A rapid test is very sensitive for doing what it is supposed to do, identifying periods of infectiousness.

Michael Mina has done a great job promoting rapid tests and I do think we are beginning to see some recognition of the difference between infected versus infectious and the importance of testing for the latter. What is frustrating is how long it has taken to get this point across. Paul Romer made all the key points in March! (Tyler and myself have also been pushing this view for a long time).

In particular, back in March, Paul showed that frequent was much more important than sensitive and he was calling for millions of tests a day. At the time, he was discounted for supposedly not focusing enough on false negatives, even though he showed that false negatives don’t matter very much for infection control. People also claimed that millions of tests a day was impossible (Reagents!, Swabs!, Bottlenecks!) and they weren’t impressed when Paul responded ‘throw some soft drink money at the problem and the market will solve it!’. Paul, however, has turned out be correct. We don’t have these tests yet but it is now clear that there is no technological or economic barrier to millions of tests a day.

Go yell at your member of Congress.

Three areas where you never run out of great books to read

Those three areas are:

1. The history of the British Isles

2. The history of the Jews, and

3. The history of World War II

Each area has attracted remarkable talent, mostly in English I should add, and you can always read yet another great book in these areas, even if you already have consumed many stellar offerings.

Whether you should double down in these areas, or strike out and diversify into the many other areas with lower quality expected return, is in fact a key question when it comes to how to read.

(Of course, a small number of books cover all three areas, though I would not suggest that they get triple credit.)

Are there any other such areas I am missing?  Somehow American history does not do it for me — too much stupidity, repetition, and needlessly “clampdown patriotic” perspectives.

“Israel Versus Anyone”

That is the title of a new research paper by Kenneth S. Brower, focusing on the capabilities of the Israeli military against various potential adversaries.  I do not myself have particular opinions on these questions, but I found this piece interesting throughout.  Here is one excerpt:

The simple and unarguable truth is that for decades the US military has lacked the ability to quickly project conventional ground and air forces into the Middle East that would be able to successfully defend Israel. This has been true for about 50 years.

The US Army and US Marine Corps combined now have an active force structure of just 39 maneuver brigades, of which only about 13 are combat ready. It would require many weeks to bring a portion of the remaining 26 active maneuver brigades to combat ready status. Achieving this would require cannibalization of about 25% of the remaining active units in order to bring the others to full strength. US reserve National Guard maneuver brigades would each require about five months for mobilization, retraining, and deployment. These National Guard reserve units are thus irrelevant to any Israeli rescue scenario.

The ability of the US military to deploy forces over long distances has declined in the last 30 years because of a lack of investment in large specialized roll-on roll-off ships. Many of the existing US reserve merchant marine ships dedicated to military use are overage and have been poorly maintained. Based on the deployment times achieved during Operation Desert Storm, it is estimated that within about three weeks the US could project two light infantry paratroop brigades into Israel by air, plus one Marine infantry brigade transferred by forward deployed USN amphibious ships and pre-loaded forward-based maritime ships. Given about nine weeks, the US would likely be able to field nine maneuver brigades in the Middle East consisting of three paratroop, three Marine, and three heavy armored brigades. Consequently, it would require about nine weeks for the US military to generate roughly 15% of the IDF’s ground force mobilizable order of battle. These US forces would only deploy about 10% of the number of armored fighting vehicles the IDF can field.

The USAF has a very limited number of combat aircraft currently deployed in Europe. With air-to-air refueling, it is estimated that these aircraft might be able to sustain the generation of about 90 sorties a day in support of Israel. But these few sorties, which only  14 I Israel Versus Anyone: A Military Net Assessment of the Middle East represent 5% of Israeli wartime capability, could only be generated if the host country where these aircraft are based were to allow them to be operated in support of Israel. In the past, this approval has not always been provided. Neither the USN nor USMC currently have any operational combat aircraft based on aircraft carriers or large amphibious ships that are normally deployed in the Mediterranean within range of Israel.

Via Adam K.

Claims about Gudrid Thorbjarnardóttir

Viking society wasn’t homogeneous. They had dealings with many different cultures and they lived in varied environments, from Danish and Swedish pasture to the sub-Arctic tundra of Norway and Iceland. In the early 11th century the best-travelled woman in the world must have been Gudrid Thorbjarnardóttir, whose remarkable journeys demonstrate the great distances the Vikings covered. She gave birth to a child in North America, met people of the First Nations and ate grapes in Vinland, made a pilgrimage to Rome and drank wine in Italy, and died as a nun in Iceland. Vikings lived in close contact with the Sámi people, whom they called Finns. In his earlier book, The Viking Way, Price pointed out that Norwegians and Swedes, at least, might be regarded as in some ways similar to the ‘circumpolar’ cultures which stretch from Greenland to Siberia, notably in what looks like shamanistic behaviour.

That is from Tom Shippey’s excellent LRB Vikings book review, interesting throughout.

No brain drain for Filipino nurses

We exploit changes in U.S. visa policies for nurses to measure brain drain versus gain. Combining data on all migrant departures and postsecondary institutions in the Philippines, we show that nursing enrollment and graduation increased substantially in response to greater U.S. demand for nurses. The supply of nursing programs expanded to accommodate this increase. Nurse quality, measured by licensure exam pass rates, declined. Despite this, for each nurse migrant, 10 additional nurses were licensed. New nurses switched from other degree types, but graduated at higher rates than they would have otherwise, thus increasing the human capital stock in the Philippines.

That is from a new paper by Paolo Abarcar and Caroline Theoharides, via Chris Blattman.