The COVID-19 pandemic has sparked a surge in interest in studying outbreaks of other infectious diseases, most notably how the introduction of control measures can change the course of the epidemic. Mathematical statisticians Olga Krylova and David Earn from McMaster University (Canada), whose article published In the magazine PLOS Biologyanalyzed from this point of view the history of smallpox epidemics that regularly occurred in London for almost 300 years.
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Scientists looked at more than 13,000 weekly smallpox deaths in London from 1664 to 1930 and found that the length of time between outbreaks, the strength of these outbreaks, and even their seasonality varied over the centuries. Moreover, many of these changes were directly related to the introduction of various measures to control infection, primarily variolation and vaccination (vaccine from smallpox was invented in 1796).
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Before the advent of the vaccine, the usual practice in London was variolation – the deliberate infection with a low dose of live virus, which made it possible to get a mild illness and get lifelong immunity. The risk of death with variolation persisted, but was significantly lower than with natural infection with smallpox virus. In this regard, there have been suggestions that the mass wearing of masks that pass low doses of the virus during the COVID-19 pandemic may become an approximate analogue of variolation.
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As a result, as the analysis of the collected data showed, it was possible to practically nullify the death rate from smallpox and the outbreaks of infection themselves by the early to mid-20th century only thanks to the mass vaccination of the population, which began in the second half of the 19th century.
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