Corona Daily 086: Miscarrying Cows

In the beginning of the twentieth century, USA had an epidemic among cows. A bacterial infection called brucellosis was spreading through the cattle, causing spontaneous miscarriages, known as “contagious abortion”. By the 1910s, the miscarriages threatened livestock across the USA.

Worried about the disease, farmers would kill the diseased animals, to try to eradicate bacteria from their herds. George Potter, a vet from Kansas had an epiphany: a cow getting brucellosis may lose its calf, but at the same time acquire immunity to the disease. An immune cow was more valuable than an uninfected one.

In a 1918 article in the Lancet, Potter compared the miscarriage disease to a fire, which unless new fuel is constantly added, dies down. “Herd immunity is developed, thereby retaining the immune cows, raising the calves and avoiding the introduction of foreign cattle. This was the first known use of the term “Herd Immunity”.

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In the 1920s this concept made some scientists curious. They began deliberately infecting mice to see how the disease spread through their colonies. They discovered that above a certain threshold, the infection couldn’t find new hosts, and stopped spreading.

In 1923, a British pathologist Sheldon Dudley studied a diphtheria outbreak at a crowded navy school. One thousand children of naval officers ate together in a dining hall, and slept in cramped military-style barracks. Dudley found that every time new students joined the school, the diphtheria bacteria would attack the newcomers, and an outbreak would start again. In 1924, Dudley applied, possibly for the first time, the term “herd immunity” to humans.

Now in covid times, a semi-literate person uses the expression. Equating us to cattle may sound offensive. But the term’s origin was in the herd of miscarrying cows.

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While Dudley was studying diphtheria, a diphtheria vaccine was developed. He began wondering: What is the best way to reach herd immunity: natural exposure or vaccination?

Last year, several heads of states thought of reaching herd immunity through natural exposure. To be fair, there were no vaccines then. Johnson started with it in the UK. Trump’s advisor Scott Atlas, who called himself anti-Dr Fauci, recommended it. (Trump was so unengaged; he often called it herd mentality). Sweden took it as an official state policy. And Russia adopted it without an official pronouncement.

All these nations were heavily punished. The UK and USA had to rethink. Sweden acknowledged the unnecessary loss of thousands. Russia has unofficially lost more than half a million to covid.

It is possible to opt for mass natural exposure if the virus is not deadly. Without vaccinations, Indians develop herd immunity against the flu every season. Because flu is not so deadly. Covid virus kills and maims. Such a plan inevitably leads to catastrophic loss of lives and suffering. We usually look at the death count. But many infected people suffer long covid, with damaged organs. They may take years to recover, or not recover at all.

Herd immunity against covid through natural exposure is rejected by scientists as unrealistic and unethical. Vaccination is the only ethical road.

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The formula for calculating the required herd immunity percentage is 1- (1/R0), which in simple language means the more transmissible the virus, the higher is the %. For example, measles, an extremely infectious disease, has an R0 between 12 and 18, which translates into a herd immunity threshold of 92-94% of the population.

Looking at this number on a national basis is a mistake. In large countries like the USA or India, some places may be vaccinated enough to reach immunity, but less vaccinated pockets may still be vulnerable.

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Finally, when the USA or UK currently say their R0 (spreading rate) is low, it is low because of the lockdowns, masks, handwashing, and distancing. When human behavior changes; people start throwing masks away, and hugging; the R0 can go up, and with it the herd immunity % required shoots up. Coming months will show whether the joy of these nations was premature.

This is why fully vaccinating an entire nation and the entire world may be the only effective way to achieve herd immunity.

Ravi