How Many People Did the Plague Kill in History?

The best available estimate puts the total death toll from plague at more than 200 million people across all of recorded history, spanning three major pandemics and countless smaller outbreaks over roughly 1,500 years.¹ That number is staggering, but it also comes with serious caveats about how anyone could count deaths across centuries and continents with wildly different record-keeping. The real figure could be higher or lower by tens of millions, and the story behind the counting is nearly as interesting as the toll itself.

The First Pandemic and the Plague of Justinian

The first recognized plague pandemic began in 541 CE, when the disease struck the Byzantine Empire under Emperor Justinian I. For centuries, historians treated this as a catastrophe on par with the Black Death, claiming tens of millions of deaths across the Mediterranean and Europe over the roughly two centuries that outbreaks continued.² That narrative has come under serious challenge. A reappraisal of the archaeological, textual, and economic evidence argues that the traditional picture does not fit the data, and that the Justinianic Plague may have been far less deadly at a population level than long assumed.

That does not mean it was gentle. Modeling work focused on Constantinople, the Byzantine capital, suggests that a single outbreak there could have killed roughly 250,000 to 340,000 people, representing somewhere around 63 to 68 percent of the city’s population.³ Those are horrifying numbers for a single city. But scaling from one dense urban center to the entire Mediterranean world is where the estimates become shaky, and where the debate about total deaths from the first pandemic remains unresolved.

The Black Death

The second pandemic is the one that dominates the history books, and for good reason. The Black Death arrived in Europe around 1347 and swept the continent in roughly four years, killing an estimated 30 to 50 percent of the European population.⁴ In absolute numbers, researchers have placed the toll at somewhere between 75 and 200 million people across Europe alone.⁵ The wide range reflects the enormous difficulty of counting medieval populations with any precision.

The devastation was not evenly distributed. Some towns lost nearly everyone. Others, for reasons still debated, escaped with lighter casualties. Analysis of skeletal remains from a Black Death cemetery in London shows that the risk of dying during the epidemic increased with age, following a pattern that roughly mirrors normal medieval mortality, where older adults were more vulnerable.⁶ This finding has surprised some researchers, because a common assumption was that the Black Death killed indiscriminately across all age groups. It was devastating for everyone, but not uniformly so.

Centuries of Recurring Waves

The Black Death was only the opening act of the second pandemic. Plague did not simply arrive, kill, and leave. It returned again and again in waves that struck European, Middle Eastern, and North African cities for centuries. In Egypt, plague recurred roughly once every two years between the Black Death of 1348 and the end of the Mamluk period in 1517, amounting to 73 recorded outbreaks in 169 years. Syria experienced about 41 outbreaks in the same period, averaging one every four years.⁷

Individual outbreaks could still be savage. Cairo, which held an estimated 200,000 residents in the 1400s, lost roughly 90,000 people in the 1430 outbreak and about 80,000 in 1460, according to contemporary sources.⁷ Even if those figures are rounded or inflated, they represent losses on a scale that would reshape a city’s economy, labor force, and social fabric for decades. European cities experienced similar cycles. The Great Plague of London in 1665, the epidemics in Marseille, Moscow, and dozens of other cities all belonged to the same long second pandemic, which did not truly end until the early 1800s in most of Europe.

The Third Pandemic

The third pandemic is the most recent and the best documented. It originated in Yunnan Province in southwestern China, where it had been circulating since at least the late 1700s. It spread to the Chinese coast in the second half of the nineteenth century, reaching Canton (Guangzhou) in 1894 and killing roughly 70,000 people there.⁸ From Canton the disease boarded steamships and reached port cities around the world, from Hong Kong to Bombay to San Francisco.

India bore the heaviest toll. An estimated 12 million people died from plague in India between 1898 and 1918.¹ The third pandemic as a whole is estimated to have killed roughly 2.2 million people, though the Indian toll alone suggests that the global figure was higher and depends heavily on how the boundaries of the pandemic are drawn.⁸ The third pandemic also gave modern science its first real understanding of how plague spreads. It was during the Hong Kong outbreak of 1894 that the bacterium Yersinia pestis was identified, and soon afterward its transmission through fleas and rodents was established.

Why the Numbers Are So Uncertain

Every headline figure about plague deaths carries a margin of error that would be unacceptable in modern epidemiology. The most widely cited numbers for events like the Black Death come from a surprisingly simple method: take population estimates from before the crisis and after it, project growth rates forward and backward, and attribute the gap to the disaster. Researchers who have examined this approach closely find that it often produces estimates that miss the real toll by large and unpredictable margins, because even small errors in the starting population figures or the assumed growth rates get magnified dramatically.⁹

This matters because the same method underlies not just plague estimates but also prominent death toll figures for the 1918 influenza pandemic, the Great Chinese Famine, and other major crises. For medieval plague, the inputs are especially unreliable. We do not have census data for fourteenth-century Europe. We have tax records, parish burial registers in some regions, and scattered chronicle accounts, many written by people who had every reason to exaggerate the horror. The range of 75 to 200 million for the entire second pandemic reflects this uncertainty honestly; a single precise number would be false confidence.

Climate and the Geography of Outbreaks

Plague does not erupt in a vacuum. The bacterium circulates in wild rodent populations, and shifts in climate can push those rodent populations into closer contact with humans. Research on the second pandemic’s recurring waves in Europe found a striking pattern: climate fluctuations recorded in tree-ring data from Central Asia preceded plague reintroductions into Europe by about 15 years. The statistical link was strong enough that specific warming-then-cooling sequences in the tree-ring record predicted 11 out of 16 documented reintroduction events.¹⁰ The implication is that plague did not simply persist in European rat populations for centuries. Instead, it may have been repeatedly reintroduced from Central Asian reservoirs, carried westward along trade routes after climate disruptions destabilized rodent ecology.

During the third pandemic, the relationship between climate and plague played out differently depending on geography. In northern China, which has an arid climate, plague cases tended to increase when conditions got wetter, likely because more rainfall supported larger rodent populations. In southern China, which is already humid, the pattern reversed: wetter conditions generally meant fewer plague cases, except during extreme rainfall.⁸ The relationship between weather and plague is not a simple equation but a set of regional feedback loops, mediated by which rodent species are present and how those species respond to moisture, temperature, and food availability.

Plague Before the Pandemics

The three pandemics account for the vast majority of documented plague deaths, but Yersinia pestis was infecting humans long before the Plague of Justinian. Genetic analysis of ancient remains has recovered Y. pestis DNA from individuals dating back roughly 5,000 years, spanning a wide geographic range across Eurasia. These early strains appear to represent a single lineage that persisted for millennia and spread across continents, but crucially lacked the genetic adaptations for efficient flea-borne transmission that made later pandemics so explosive.¹¹

Without flea transmission, these early forms of plague likely spread through other routes, possibly respiratory droplets or direct contact with infected animals. They could still kill, but they would not have caused the same kind of runaway urban epidemics seen in later centuries. The discovery of a flea-adapted form of Y. pestis in Bronze Age Iberia pushed back the timeline for that adaptation, suggesting it was already circulating in parts of western Europe earlier than previously thought. How many people these pre-pandemic strains killed is genuinely unknowable, and they are not included in the 200 million figure.

Plague in the Modern World

Plague did not vanish after the third pandemic faded. The World Health Organization still receives reports of plague cases every year, mostly from Africa, and Madagascar remains a particular hotspot. Plague has been endemic in the Madagascan highlands since the 1920s, with annual case numbers in recent decades fluctuating between about 100 and 700. In years linked to strong El Niño events, the numbers have spiked dramatically, reaching nearly 3,000 reported cases in 1997.¹²

The difference between medieval plague and modern plague is largely about treatment. Before antibiotics existed, plague mortality in the United States ran around 66 percent. After antibiotics became available, that dropped to about 16 percent overall. Among patients treated with the most effective drugs, mortality fell further to around 9 percent. Patients who received only less effective antibiotics still faced a 51 percent fatality rate.¹³ Among specific drug classes, tetracycline-treated patients in one review had a zero percent case fatality rate, while sulfonamide monotherapy was associated with fatality rates above 20 percent.¹⁴ Speed of treatment matters enormously. Plague is still lethal if you do not get antibiotics quickly, but with prompt treatment it is now a survivable infection for most patients.

How the Black Death Reshaped Human DNA

When you kill 30 to 50 percent of a population, you do not just change demographics. You change the gene pool. Researchers studying DNA from medieval London plague victims, along with remains from before and after the Black Death, found that immune-related genes were strongly enriched among the genetic sites showing the biggest shifts between the pre-plague and post-plague populations. The study identified 245 genetic variants that were highly differentiated in the London dataset, with four replicated in an independent cohort from Denmark.¹⁵

One gene in particular stood out. A variant near a gene called ERAP2 appeared to give its carriers a survival advantage during the Black Death. The selected version of this gene is associated with producing a full-length version of a protein involved in immune signaling, and laboratory experiments showed that it enhanced the ability of immune cells to control Y. pestis inside the body.¹⁶ Separate analysis of plague victims from sixteenth-century Germany found similar shifts in immune gene frequencies, including changes in the HLA region, which plays a central role in how the immune system recognizes threats.¹⁷

The twist is that these protective plague-survival variants overlap with alleles now associated with higher susceptibility to autoimmune diseases like Crohn’s disease and rheumatoid arthritis.¹⁵ An immune system primed to fight off Y. pestis more aggressively may also be more likely to attack the body’s own tissues. The Black Death, in other words, did not just kill 200 million people over the course of its pandemic. It left a biological signature in the survivors’ descendants that is still shaping patterns of disease today, centuries after the last major European outbreak.

1
PubMed Central. History of the Plague: An Ancient Pandemic for the Age of COVID-19
2
PubMed Central. The Justinianic Plague: An inconsequential pandemic?
3
PLOS ONE. Modeling the Justinianic Plague: Comparing hypothesized transmission routes
4
PubMed Central. Mortality Risk and Survival in the Aftermath of the Medieval Black Death
5
Humanities and Social Sciences Communications. Conflicts and the spread of plagues in pre-industrial Europe
6
PubMed Central. Age Patterns of Mortality During the Black Death in London, A.D. 1349–1350
7
Cairn.info. Refugees of the Black Death: Quantifying rural migration for plague and other environmental disasters
8
PubMed Central. Nonlinear effect of climate on plague during the third pandemic in China
9
Demographic Research. Can we estimate crisis death tolls by subtracting total population estimates? A critical review and appraisal
10
PubMed Central. Climate-driven introduction of the Black Death and successive plague reintroductions into Europe
11
PubMed Central. Stone Age Yersinia pestis genomes shed light on the early evolution, diversity, and ecology of plague
12
PubMed Central. Factors influencing the re-emergence of plague in Madagascar
13
Clinical Infectious Diseases. Antimicrobial Treatment Patterns and Illness Outcome Among United States Patients With Plague, 1942–2018
14
Clinical Infectious Diseases. Treatment of Human Plague: A Systematic Review of Published Aggregate Data on Antimicrobial Efficacy, 1939–2019
15
PubMed Central. Evolution of immune genes is associated with the Black Death
16
Nature. Evolution of immune genes is associated with the Black Death
17
Molecular Biology and Evolution. Analysis of Genomic DNA from Medieval Plague Victims Suggests Long-Term Effect of Yersinia pestis on Human Immunity Genes