What 3 centuries of smallpox mortality data shows about how epidemics linger

Researchers pored over weekly reports of deaths in London to get a centuries-long view of how and when smallpox outbreaks ravaged the city.

(CNN)As so many people around the globe contemplate what their lives might look like after the pandemic, new research on smallpox might help provide insight.

Researchers revealed nearly three centuries of data showing repeated smallpox epidemics in London in a study published Monday in the open access journal PLOS One.
"This study reveals detailed patterns of extremely important infectious disease, over a very long period -- much longer than any human lifetime," said lead study author David Earn, a professor of mathematics at McMaster University in Hamilton, Ontario.
The smallpox story is a sobering reminder of a not-too-distant reality: The monthslong wait for the expedited Covid-19 vaccine pales in comparison to centuries in which smallpox was rampant.
"Smallpox was ... staggering in comparison to what we're talking about now. I mean, there's just no comparison of the level of devastation and fear this disease caused," he said.
With the help of his colleagues and undergraduate research assistants, Earn -- over the course of the last few years -- digitized 13,000 weekly smallpox mortality records.
"I've looked at annual counts of smallpox, but not these weekly counts and the weekly counts reveal the full structure of the epidemics, how fast each epidemic took off exactly," Earn said. "The shape of the epidemic curve was completely hidden before this."

Hundreds of years of data

Left untreated, smallpox would kill three out of every 10 who were infected with it, according to the Centers for Disease Control and Prevention. And those who survived often lived with scars afterward.
The new study follows research Earn has published on the historical spread of diseases such as bubonic plague, cholera and scarlet fever.
His team's goal was to make these records publicly available and enable scientists to analyze how patterns of disease spread in populations. Many historic trends can alter disease spread. Natural forces, such as the weather or the changing of the seasons, can drive an outbreak.
And then there are social factors: population density, population structure, the introduction of schools and the course of wars.
The data spans 267 years, from 1664 to 1930, the last year in which there was more than one smallpox death in a single week. London's last death from the disease occurred in 1934.
The researchers were particularly interested in the seasonality of smallpox outbreaks. In the 17th century, the team observed, epidemics primarily occurred in the summer or early fall. But by the 18th century, those outbreaks were shifting to appear in late fall or early winter.
Even a cursory glance at the 17th century records is a window into another era, in which other causes of death include "wormes," "jaundies," "spleen," "lethargy" and "frighted." A September 1665 page, for instance, lists "teeth" as one of the other leading causes of death behind bubonic plague.
One death that week was in the oddly specific category for "burnt in his bed by a candle at St. Giles Cripplegate."
The weekly bills of mortality were only published for a few towns. The researchers analyzed data from the London bills of mortality, which were compiled from Anglican Church funeral records.
While those records don't capture every London death -- they could have missed fatalities occurring outside the city or without a church burial -- the records do give a fairly precise accounting of the rise and fall of smallpox over the years.
For deaths from 1842 onward, the researchers used the Registrar General's Weekly Return statistics for a more thorough accounting.
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