In the current pandemic, scientists have drawn attention to the only disease of humanity that we have successfully defeated, namely smallpox. The results of a recent study published in PLOS Biology.
Even today, four decades after smallpox stopped spreading among the population, the disease is still considered one of the greatest killers in history. It has claimed more lives over the centuries than any other infectious disease, even plague and cholera.
In the 18th century, 400,000 Europeans died of smallpox every year. In London alone, after 1664, more than 321 thousand people died from the disease.
A third of the survivors were left blind, and many others were disfigured with scars.
“The current COVID-19 pandemic has sparked a resurgence of interest in studying infectious disease transmission and how public health protections can change the course of the pandemic.” is talking David Earn, who is modeling infectious disease transmission at McMaster University in Ontario.
For nearly 300 years, between 1664 and 1930, the authorities in London kept a careful record of smallpox deaths. Digitizing over 13,000 of these weekly reports, the researchers have created a massive timeline of smallpox deaths and prevention, tracking the movements of the virus in London and how seasons, public health policies and historical events affected the spread of the disease.
In earlier records, outbreaks appeared sporadically, gradually turning into regular streams of infection reports by 1770, when a primitive form of smallpox vaccination called variolation began to gain popularity.
It was not until 1810, when safer vaccination practices were introduced, that data show a sharp decline in the amplitude of epidemics, although outbreaks have become more frequent.
A particularly large epidemic in London in the 1830s, which eventually spread to all of Europe, actually became the impetus for the adoption of England’s first vaccination law in 1840, which gave free vaccinations to everyone and banned more dangerous methods such as variolation. Only after that did the number of deaths drop sharply.
In the years leading up to the last smallpox death in London, around 1934, there were only a handful of deaths from the virus.
“It’s clear that the introduction of smallpox control measures — vaccination and then vaccination — made it possible to eradicate it,” says Olga Krylova, who worked on the project at McMaster University. “Our analysis also shows that increased use of control measures and changes in public health policies have been correlated with changes in the frequency of epidemics.”
The last case of smallpox infection in vivo was recorded on October 26, 1977 in the Somali city of Marka. And in the summer of 1978, the most recent known case of smallpox was an intralaboratory infection that took the life of 40-year-old Janet Parker, a medical photographer. Now the last remaining smallpox samples are stored in the United States and Russia.
Over the centuries London has undergone a number of major cultural and historical changes. The Industrial Revolution, for example, may have played a role in the smallpox epidemic as urbanization spread and social demographics changed. Wars were another possible propagation mechanism.
“Further research is needed using mathematical models to quantify the impact of interventions and historical events on smallpox outbreaks,” says Krylova.
Examining this data can give us insight into how the pandemic is changing over time and moving from a deadly threat to a historical artifact.
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