On infection parties, herd immunity and other half-truths

Anita Guerrini | 08 April 2020

On 25 March, the conservative US magazine The Federalist published an article by Oregon dermatologist Douglas Perednia suggesting that young people should deliberately infect themselves with coronavirus in order to induce herd immunity. The prime ministers of Great Britain and the Netherlands have previously touted herd immunity as a way to slow the spread of the virus while avoiding the social distancing that has become the norm, to the detriment of global economies. Dr Perednia claims that anyone over 60 remembers when parents would convene “chickenpox parties” to infect their children so that they could get it all out of the way at once. I must admit that I am over 60 and I never heard of this practice. As a historian of medicine, however, I have heard about smallpox parties in the eighteenth century. I suggest that these are not a terribly good model for containing coronavirus.

Smallpox remains the only disease that has been completely eradicated from the globe, an achievement made official by the WHO in 1980. A concerted global effort over a decade vaccinated enough people to induce herd immunity; depending on the disease, this requires 85-95% of the population to be immune from the disease. Herd immunity breaks the chain of transmission because there are too few people to pass the disease on.

The English physician Edward Jenner developed the first smallpox vaccine at the end of the eighteenth century after he noticed that those who had been infected with cowpox, a much milder disease, became immune to smallpox. 

Smallpox was among the most feared diseases in the world. Like coronavirus, it was highly contagious and could be spread by droplets in the air as well as contact with infected surfaces. It was deadly, with mortality rates ranging from 2% to 50% or even higher among previously unexposed populations. Survivors of smallpox suffered facial and bodily disfigurement and at times blindness from the rash. Children were particularly susceptible.

However, survivors were generally immune from further attacks. Before the vaccine, in some parts of the world people deliberately induced the disease in the hope that the case would be mild and would produce immunity. Parents practiced “buying the pox,” sending their children to a victim of a mild case to purchase a few scabs fallen from the smallpox pustules. These would either be ground up and inhaled or inserted into a scratch on the arm.  However, no one understood precisely how the disease was contracted or how immunity worked. 

European scientific journals began to report these practices in the early eighteenth century. In New England, the prominent minister Cotton Mather (1663-1728) promoted inoculation – later called variolation from the Latin word for smallpox, variola – during the 1721 smallpox epidemic in Boston. In England, Lady Mary Wortley Montagu (1689-1762) brought the practice back from Constantinople, where her husband had been ambassador, and had her children inoculated. 

Variolation became widespread in Europe. Nevertheless, it was risky. The severity of the induced cases was largely a matter of luck; the death rate among inoculated cases was 0.5 to 2%, far below the rate for natural smallpox but nonetheless far from negligible. In comparison, the death rate for seasonal flu is about 0.1%, amounting to some 23,000 deaths so far this year in the US. Moreover, those inoculated contracted smallpox, and therefore could, and did, infect other people. People feared smallpox so much, however, that they were willing to take the risk.

Following three centuries of research on viruses, we now have a much better, although still incomplete, idea of how they work. Because the coronavirus is a new mutation, a lot remains unknown. We do not know if it is seasonal, like the flu, or even if contracting COVID-19 induces immunity; there are anecdotal cases that suggest that this is not always true. The death rate for COVID-19 is around 2%, but that appears to vary widely depending on location and the age of the patient, with older people experiencing rates of 10-15%.  If we reach a million cases in the US, far below the 38 million cases of flu, this could mean, at the low end, 20,000 deaths. 

Those promoting “coronavirus parties” among the young assert that statistically they are at low risk for severe illness or death, and that a 14-day confinement period is adequate to show signs of infection. Neither of these assertions can be conclusively proven from the very inadequate data we now possess. Quite apart from the ethical problems with deliberately making people sick – even volunteers (look up Walter Reed and yellow fever) – the prospect of unleashing new cases of COVID-19 onto the public is all too probable. Rather than leading to herd immunity, it could lead to herd mortality. Is the stock market really worth it? 

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• Guerrini, Anita
• Medicine and public health
• Covid-19

About the author

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Anita Guerrini is Horning Professor in the Humanities Emerita at Oregon State University.  A historian of science and medicine, she has taught courses on the history of infectious disease and on disease and the environment for over thirty years.