– May 11, 2020

The expression “herd immunity” is misleading. Instead we should speak in a looser way of augmented immunity. 

The war on COVID-19 should not be waged as a big centrally commanded confrontation. It should be waged as guerilla warfare while making strides in augmented immunity.

The concept of herd immunity highlights that as the immunity rate among a population is augmented the rates of transmission decline and, past some point, drive toward elimination of the disease. But herd immunity obscures important aspects of the problem, including how transmission of the disease is affected by behavioral changes and how the disease affects people differently. 

Dictionary.com says for the word herd:

a number of animals kept, feeding, or traveling together; drove; flock: a herd of cattle; a herd of sheep; a herd of zebras.

If one thinks of a herd of cattle, one does not think of separations within the population. “Herd” connotes that there is no such separation! All of the cattle are herded together.

But one key tactic to fighting COVID-19 is to keep the vulnerable separate from the rest of the population. We should not view the national population as a herd.

When herd immunity has been reached, we say the epidemic has ended. But that does not mean the fight is over. A COVID-19 infected staff worker still could enter a nursing home and kill dozens of people. The guerilla warfare must continue even after the threshold for herd immunity has been reached.

Let’s look at Wikipedia’s definition of herd immunity. It is based on a threshold condition where the still-susceptible proportion of the population multiplied by R0 equals 1. 

What is R0? It is “the average number of new infections caused by each case in an entirely susceptible population that is homogeneous, or well-mixed” (Wikipedia, italics added). 

Well-mixed is what we strive to prevent! We strive to separate the vulnerable from the rest of the population.

And the population is not homogeneous – far from it! For most people COVID-19 is scarcely a disease at all!

As for “the average number of new infections caused by each case:” That is being cranked downward by the behavioral changes everyone is making.

Every country will find its way out of the mess, reaching a state of affairs that then will be declared, “herd immunity.” What, then, is the challenge that society faces? 

We are trying to make the path better rather than worse. 

The lockdown path shuns augmented immunity. That path will be protracted and catastrophic

A better path is one like that of Sweden, seeking augmented immunity and leaving the fight to decentralized guerilla fighters, each acting in his or her corner of the struggle, according to the local conditions and particular hazards. 

Sweden has not done a good job in protecting its most vulnerable, particularly in elderly care. Everyone was caught unprepared, officials and staff workers were slow to make adjustments, and lessons are being learned. 

Whatever the failings there, Sweden’s permissive approach for society as a whole is the right one. Despite failures in particular corners of the war, Sweden is finding a better path out of the mess.

If the right people—not elderly, not ailing—get the disease and adjust behavior suitably while contagious, it is good that they get it behind them. That will enable them to resume their important roles in the health and well-being of society. 

As we learn more about protecting from the virus and as we develop new and better ways to work around contagion, the justification for general lockdowns grows weaker and weaker. The vulnerable people are already in a much better position to protect themselves against the virus. 

The best approach is like guerilla warfare carried out by local militias, not a D-Day invasion or a siege on the city. The guerilla tactics are diverse, continually adjusted, even yet to be discovered. They include scouting for hotspots, testing and  monitoring for symptoms, using protective equipment, social distancing, self-quarantining when appropriate, shielding the vulnerable, washing your hands, developing better therapeutics, allowing human challenge trials for vaccine development, and many other tactics.

But also and most importantly: Augmenting immunity among the right people. 

The guerilla fighters are all of us.

Daniel B. Klein

Daniel B Klein

Daniel Klein is professor of economics and JIN Chair at the Mercatus Center at George Mason University, where he leads a program in Adam Smith. He is also associate fellow at the Ratio Institute (Stockholm) and chief editor of Econ Journal Watch.

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