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The herd ensures the survival of only some individuals

“He fell in October, 1918…turning him over one saw that he could not have suffered long…”  — Erich Maria Remarque, All Quiet on the Western Front

When will all this fear, suffering and chaos end? When will the COVID-19 pandemic pass, making it safe to return to normal social behavior? 

Unfortunately, for the approximately 75 million Americans who are over 60 years old, the answer might be, “at least a year from now.” Statistically, those citizens are among the most vulnerable to life-threatening COVID-19 infections. Anyone in that group should studiously avoid exposure to the virus until a preventive vaccine and, ideally, a penicillin-like cure for the disease becomes widely available.

Four to six months from now some of the younger, previously infected survivors of mild to moderate COVID-19 infections could return to some types of non-essential work — provided they took an antibody blood test establishing they’d had the disease and there was reliable evidence showing that their infection response created immunity. (Fast, cheap antibody tests are being developed and should be deployed in a few months.) However, there will not be enough people available to effectively “reopen the economy” until we have achieved sufficient “herd immunity” to mostly check the spread of the contagion. 

What does that mean?

According to the (accurate) definition in the Wikipedia article Herd Immunity, “Herd immunity is a form of indirect protection from infectious disease that occurs when a large percentage of a population becomes immune to an infection, whether through previous infections or vaccination, thereby providing a measure of protection for individuals who are not immune.” 

It works like this: Say in a total population of 100 people, 75 individuals are immune to disease “X.” If someone catches X, chances are that three out of four people she encounters will be immune to the disease and will not contract and spread it (although they could spread it if, like coronavirus, it survived on their hands and could be transmitted by direct contact). X would only be caught and potentially spread by those who are not already immune. 

According to Science Media Center’s Professor of Medicine Paul Hunter, “A disease’s ‘Reproductive Ratio’ (Ro), “is the number of people who are likely to be infected by a single case when a new pathogen appears in a community with no prior immunity.” If a pathogen’s Ro = 2, the first case will infect two people, and each subsequent case will infect two more, creating an infection sequence of 2, then 4, then 8, and so on. But if 50% of the population is immune, then on average one case will infect only one person. Therefore, the sequence 1, 2, 4, 8, 16… becomes 1, 1, 1, 1… “and the disease will die out fairly quickly,” Hunter concludes.

For COVID-19, the Ro = 3 (approximately). So, for the contagion to be (mostly) eradicated through herd immunity, roughly 67% of the population would have to be immune to the disease.

Reaching that level of COVID-19 immunity through a combination of natural contagion and vaccination would likely take at least nine months, possibly as many as 18. Ironically, the more we protect ourselves through social distancing, the longer the contagion timeline. And 33% of the population could still get, and transmit the disease, just as millions of people in our largely-immune population get the flu every year. 

In his classic anti-war novel All Quiet on the Western Front, Erich Maria Remarque tells the story of a German infantryman who for years survives the horrors of battle on WWI’s front lines, only to make a fatal mistake just weeks before the war ends. Anyone who wants to survive the COVID-19 pandemic should remember Remarque’s story, lest he or she reenters society prematurely.

Editor’s Note: A version of this article appeared previously in other publications as part of an ongoing series called “Your Ecological House,” written by Philip S. Wenz, the publisher of Firebird Journal.

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