The quintessential infectious disease that frames our way of thinking is the medieval Black Death, which devastated Europe from 1346-1351. It killed perhaps half the population — some scholars estimate the number of dead between 75 million and 200 million — and it supposedly caused massive societal changes, including radically improved working conditions and a reshaping of the period’s art and literature. The Black Death was also the beginning of the much longer Second Plague Pandemic, which lasted until the 18th century in Europe and the 19th century in the Middle East.
From the turn of the 20th century, the Black Death gradually became the standard model for how we understood the outbreaks of infectious disease leading to the deaths of huge numbers of people. For historians, the public and even schoolchildren around the world, the Black Death symbolizes the enormous potential mortality a pandemic can cause. It also highlights the importance of modern medicine and technology today to prevent a return to the seemingly backward Middle (“Dark”) Ages. But assuming that all infectious diseases potentially have the same outcome as the Black Death would be a mistake.
Consider, for example, the history of the Justinianic Plague (c. 541-750), an earlier plague pandemic. For the past few decades, and with increasing frequency since the turn of the 21st century, many scholars interpreted the written sources for this pandemic based on the Black Death model and assumed the Justinianic Plague had similar catastrophic mortality. Estimates over the past few years have suggested that between 15 million and 25 million people died, most in just the first three years of the outbreak. Science has demonstrated that the same bacterium, Yersinia yersi, caused both outbreaks, bolstering arguments that, like the Black Death, the Justinianic Plague also caused significant historical events during the period, such as the fall of the Roman Empire and the rise of Islam.
But research from the past several months has revealed how scant the evidence of the Justinianic Plague’s supposedly massive impact really is. Yes, a few high-profile authors from the period described the plague, and several other written sources briefly referred to a disease outbreak. But most accounts suggested that it was hardly a killer on a catastrophic scale. Instead, they described the plague as not unlike our flu outbreaks, with some infected people and sometimes elevated numbers of deaths. And the vast majority of authors during the period did not even mention plague.
The most recent paper on the topic examined large quantitative data sets of graves, ancient DNA, pollen and inscriptions — all things that should have shown changes caused by the deaths of half the population of the Mediterranean — and found no evidence that the Justinianic Plague transformed people’s lives. For example, if huge numbers of people had suddenly died, there should have been less time to bury them with inscribed tombstones at their graves, less money to construct new buildings with inscriptions detailing who built them and why, and fewer people who could commission and write inscriptions. But the number of inscriptions produced in Syria — a hotbed of plague, based on the few famous written accounts — remained stable both before and after the onset of plague. A few decades later, when a political disaster — the Persian conquest of Syria — occurred, the number of inscriptions instantly crashed to nearly zero, suggesting huge changes in how society operated.
Similarly, an examination of pollen collected in lake bed sediments — indicative of land use and therefore agricultural activity — found that unlike during the Black Death, there was no sudden decrease in agricultural activity. These changes should be expected if half the general population — of which probably 90 to 95 percent worked in agriculture — had died of plague. The view that there were massive numbers of deaths from 541 to 750 lacks support. Plague certainly struck the Mediterranean, but it did not seem to affect the lives of most people.
These results highlight the danger in assuming that the Justinianic Plague behaved similarly to the Black Death simply because both were caused by the same bacterium. In reality, the bacterium has caused far fewer deaths in other periods of history, and in fact still exists in the wild today, including in the western United States.
What has changed is not what plague does, but what we think it does.
Since the mid-1990s the media, scientists, the government, the security apparatus and eventually historians began to perpetuate an “outbreak narrative” about pandemic disease typified in popular culture, for example, by the 1995 movie “Outbreak.” Each of these groups had its own reasons — whether generating more stories, fundraising or identifying new national security threats. The result was a feedback loop: Studies emphasized potential dangers from infectious diseases, and it led to more research, preparedness exercises and media attention to infectious diseases, which in turn led to more research funding.
We have internalized this cultural narrative to such an extent that we replay it as a script with each new outbreak — whether real or fictional. Once the pathogen’s identity is revealed to the public, a new name will become commonplace. The government will reassure the public that everything is safe (until it isn’t). Dissenters will critique the government for failing to prepare adequately. The media will publicize the identity of the source (almost always foreign), trace the pathogen’s transmission and headline the number of infected and dead. Doctors will heroically risk their lives to fight the disease and cure the pandemic.
No one yet knows whether the coronavirus will more closely resemble the Justinianic Plague or the Black Death. Instead of assuming the future effects of an outbreak based on a cherry-picked past precedent (the Black Death), perhaps a better way forward would be to follow the Justinianic Plague example and evaluate each infectious disease based on what it actually does and not what we assume it should do or what we fear it might do.