What were the death tolls from pandemics in history? - Our World in Data

Pandemics have killed millions of people throughout history. How many deaths were caused by different pandemics, and how have researchers estimated their death tolls?

COVID-19 has brought the reality of pandemics to the forefront of public consciousness. But pandemics have afflicted humanity for millennia. Time and again, people faced outbreaks of diseases – including influenza, cholera, bubonic plague, smallpox, and measles – that spread far and caused death and devastation.

Our ancestors were largely powerless against these diseases and unable to evaluate their true toll on the population. Without good record-keeping of the number of cases and deaths, the impact of outbreaks was underrecognized or even forgotten. The result is that we tend to underestimate the frequency and severity of pandemics in history.

Often, we have records of epidemics occurring in some countries but lack good records from other regions, despite knowing that the geographical impact of the disease would have been very wide. Additionally, we often lack knowledge about which pathogens caused outbreaks and, thus, if a historical event can be considered a pandemic or if it consisted of parallel outbreaks of different diseases.

To deal with the lack of historical records on total death tolls, modern historians, epidemiologists, and demographic researchers have used various sources and methods to estimate their death tolls – such as using data from death records, tax registers, land use, archaeological records, epidemiological modeling, and more.

In this article, I present the various methods they rely on and visualize the estimated impact of what are now considered the major pandemics in history.

Although there is no universally accepted definition of a pandemic¹, diseases called pandemics share several characteristics.

Pandemics generally refer to diseases with a vast geographic range – such as spreading across a continent or multiple continents. In addition, they tend to describe outbreaks that are rapidly growing or expanding in range; highly infectious; affecting a large number of people; and caused by novel pathogens against which there is little or no pre-existing immunity.²

Researchers have estimated the death tolls of pandemics in different ways, depending on the data available.

Some death tolls have been estimated by looking at excess deaths: researchers estimate the additional number of deaths that occurred during a pandemic compared to the expected number of deaths in a typical year. This can be helpful to understand the pandemic's overall impact, even if records from death certificates are unavailable.

For some pandemics, death tolls are estimated from the net population reduction, where researchers calculate the difference in population size before and after the pandemic. This is often used for severe events – such as the Columbian Exchange – where a significant fraction of the population died.

Some death tolls have been estimated through epidemiological modeling – based on knowledge of the transmission of the disease and its geographical spread, its fatality rate (the share of people affected who die from it), access to treatment, and other types of data.

Finally, some death tolls have been calculated only using recorded deaths (also referred to as 'confirmed deaths'). This is the number of deaths officially reported with the disease as their cause of death. This method may vastly underestimate the number of deaths caused by the pandemic, as comprehensive historical records are lacking. Even today, cause-of-death registration is lacking in many parts of the world, which is one reason why the number of confirmed deaths from COVID-19 is much lower than the total death toll from the pandemic.

I have brought together estimates of death tolls from different pandemics in history for this article, which we have visualized in a timeline below.

The size of each circle represents one pandemic's estimated death toll. Pandemics without a known death toll are depicted with triangles.

This overview shows us the vast impact that pandemics have had over history.

You can see that the largest pandemics – such as the Black Death – killed more than half of the population. Several pandemics have swept through the population repeatedly: in just the last two hundred years, seven major pandemics were caused by cholera, and another seven were caused by the flu.

Pandemics devastated millions and left a shadow on those who survived. The suffering they caused may once have felt inescapable.

Before the formation of germ theory, we lacked good knowledge of pathogens that caused them, how they spread, and how to protect ourselves from them. Before molecular testing to analyze pathogens' genomes, we lacked a good understanding of how they evolved and changed over time.

Our ability to respond to pandemics has been transformed by advances in scientific understanding but truly depends on a wide range of efforts – from data collection to research and communication, public health efforts, healthcare access, and cooperation.

For example, the collection of death records allowed scientists to discover how cholera spread and how to prevent it. Coordination to address HIV/AIDS has prevented millions of deaths worldwide. Global testing for new influenza strains has helped adapt flu vaccines each year.

With better understanding, resources, and effort, much more progress can be made. The world can respond more swiftly and effectively to pandemic risks and avoid and reduce the impact of future pandemics. But without such efforts, we will continue to face major pandemics as we have experienced so far.

Dataset and sources

The full dataset and sources used in the chart can be found in our spreadsheet.

In the appendix below, I review some of the major pandemics in history and their historical impact and describe how their death tolls have been estimated.

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The Black Death

The Black Death (1346–1353 CE) – one of the earliest pandemics with a methodically estimated death toll – killed around 50–60% of Europe's population, approximately 50 million people, in just 6 years.³

Researchers have established that many people also died elsewhere – as large outbreaks are also recognizable in historical records from Western Asia, the Middle East, and North Africa – but comprehensive estimates of the global death toll are not available.

Population censuses were not conducted then, so our understanding of the Black Death's impact in Europe comes from historical records such as tax and rent registers, parish records, and archeological remains. But uncertainty remains, as these records come from a limited number of European regions and are extrapolated to the rest of the continent, based on demographic estimates.

Careful examination of these sources has led to historians revising estimates of the death toll upwards⁴ and confirmed the bacterial cause of the pandemic: Yersinia pestis (Y. pestis).⁵

People in the fourteenth century were not aware of this bacterium, nor did they know how it was transmitted – from rat fleas to humans – as this was long before the development of germ theory in the late nineteenth century.⁶

Without this knowledge, they also had little understanding of how to protect themselves, resulting in the relentless spread of the Black Death. Even after its initial wave, the pandemic continued with frequent, though smaller outbreaks until around 1690.⁷

Y. pestis caused diseases known as "bubonic" and "pneumonic" plague, where patients experienced fevers, chills, vomiting, and excruciating headaches, and distinctive "buboes" formed in their swollen lymph nodes – typically in the groin, thighs, armpits, or neck.

As Y. pestis spreads through the lymph nodes, it emits toxins that break down blood vessels and form clots, potentially blocking blood circulation and leading to death.⁸

Other bubonic plague pandemics

It is now recognized that the Black Death was not the only plague caused by Y. pestis. Genetic evidence suggests that this bacteria emerged at least 4000 years ago.⁹

The first known bubonic plague pandemic began in 541 CE and had recurrent outbreaks until the mid-8th century. This devastating pandemic affected the Eastern Roman Empire (Byzantine Empire), the Middle East, North Africa, and the Mediterranean.

The initial and most severe outbreak, known as the "Justinian Plague" (541–549 CE), was named after Emperor Justinian, who ruled Constantinople at the time.¹⁰

The third pandemic occurred between 1894 and 1940, mainly affecting Asia and Africa.

Bubonic plague is less common today due to improved sanitation and hygiene measures which reduce the density of rats and rat fleas, improved public health surveillance, and effective antibiotics, but cases have been seen even in recent years, in different continents, mainly in small towns and villages.¹¹

The Columbian Exchange

The chart shows the immense impact of the "Columbian Exchange", with an estimated 48 million deaths.

The Columbian Exchange describes the period following Christopher Columbus's voyage to the Americas in 1492 – during which populations, ideas, and crops, such as tomatoes, potatoes, and maize, spread between the Americas and the rest of the world.

But the Columbian Exchange also involved extensive war, conquest, slavery, and the spread of multiple deadly diseases, which led to the devastation of indigenous populations.¹²

Smallpox, cholera, measles, diphtheria, influenza, typhoid fever, bubonic plague, and other diseases had already killed many in Europe. But they tended to be more severe to Native Americans, who had been previously isolated from these diseases and lacked immunity to them.

The immense death toll shown on the chart is calculated as a "net population reduction" compared to the pre-1492 population size.

The Native American population was estimated to be around 54 million before Columbus's arrival. Over the following century, around 48 million died and the population had declined to 5.6 million in 1600 – a reduction of about 90%.

Both numbers are estimated by compiling data from a range of sources, including archeological records, tribal records, censuses, epidemiological modeling, and land and crop use.¹³

Influenza pandemics

Influenza (flu) pandemics arise through sudden evolutionary changes in flu viruses when different strains combine to form novel flu strains¹⁴, which can be more infectious and lethal than previous ones.

Although flu has affected humanity for thousands of years¹⁵, comprehensive death tolls have only been estimated for the flu pandemics in the last 140 years.

The largest – the 1918 "Spanish flu" pandemic – has an estimated death toll of 50 to 100 million.¹⁶ This estimate is a compilation of various historical sources, including recorded death tolls and estimates of excess deaths from different regions.

You can read more about the impact of the Spanish flu pandemic in our article:

The Spanish flu: The global impact of the largest influenza pandemic in history

The Spanish flu pandemic had a devastating impact on the global population.

The chart also shows the estimated impact of other significant flu pandemics: the 1889 "Russian flu" pandemic (an estimated 4 million deaths), the 1957 "Asian flu" pandemic (2 million), the 1968 "Hong Kong flu" pandemic (2 million), and the 2009 "Swine flu" pandemic (100,000 to 1.9 million deaths).¹⁷

Their death tolls have been estimated from excess mortality during the pandemics compared to the years immediately before and after, using available national mortality records and extrapolation to the global population.

Cholera pandemics

As the chart shows, seven cholera pandemics have occurred in the last two centuries.¹⁸ Most are considered to have originated in the Indian subcontinent and expanded across countries and continents through war, travel, and international trade.¹⁹

Our knowledge of the total global death toll from cholera in history is limited²⁰, but historical reports from across the world suggest an immense impact of the disease. For example, between 1865 and 1947, at least 23 million people died from cholera in India alone.²¹ But significant outbreaks have been recorded in many more countries.²²

Cholera is particularly severe because, if left untreated, the bacteria Vibrio cholerae can cause severe dehydration and death within hours or days of the first symptoms.²³

Its severity has been reduced with a range of scientific advances: the understanding that cholera spread through contaminated water and food, and thus that clean water and sanitation could prevent it; the identification of Vibrio cholerae as the cause; the development of antibiotics; and the knowledge that severe forms of the disease could be substantially reduced with simple rehydration treatment.²⁴

Cholera continues to kill, even today. Since 1960, over 900,000 deaths have been recorded from cholera globally as part of what's considered the "seventh cholera pandemic" – this is shown in the chart.²⁵

HIV/AIDS

When HIV/AIDS (acquired immunodeficiency syndrome) was first identified in the early 1980s, it had a fatality rate of 100%, and patients had a median survival time of about one year after being diagnosed.²⁶ It spread rapidly as the world grappled to recognize, understand, and respond to the growing epidemic.

HIV, the virus that causes AIDS, attacks white blood cells – which are critical for our immune function – and leaves patients vulnerable to a wide range of opportunistic infections and diseases.

Learn more on our page on HIV/AIDS:

HIV / AIDS

A global epidemic and the leading cause of death in some countries.

The timeline shows the enormous and continuing impact of HIV/AIDS, which has resulted in an estimated 33 million deaths worldwide between 1981 and 2022.

Our understanding of its death toll comes from available data and statistical modeling. The estimates consider various factors, such as characteristics of the virus's transmission, behavioral and clinical data, the availability of treatment, and recorded deaths from countries with high levels of death registration. ²⁷

The global response to HIV/AIDS has involved international cooperation, resource allocation, and scientific advances in antiretroviral therapy, which together have transformed HIV from a fatal diagnosis to a manageable chronic condition with treatment.

In recent years, around 1.5 million deaths have been averted annually due to the effects of antiretroviral therapy – which prevents the virus from replicating and thereby reduces the severity of the disease and its spread to other individuals.

This is shown in the chart below, along with the estimated number of HIV/AIDS deaths that still occur – around 600,000 deaths annually in recent years.

COVID-19

The COVID-19 pandemic was caused by the novel coronavirus SARS-CoV-2, which emerged at the end of 2019 and rapidly evolved into a global health emergency. Characterized by its highly infectious nature and severe respiratory symptoms, COVID-19 led to widespread illness and fatalities across the world.

The timeline above shows the vast global impact of the COVID-19 pandemic – with around 27 million excess deaths between January 2020 and November 2023.²⁸ This makes it one of the deadliest pandemics of the last century.

COVID-19's death toll has been measured by excess mortality, which describes the number of deaths above what would have been expected based on previous years.

This method is used because the global number of confirmed deaths from COVID-19 (those where COVID-19 is listed as the cause of death) is certainly much lower than the total number of deaths from COVID-19. This is because, in many countries, testing for COVID was very limited throughout the pandemic, and cause-of-death registration was, and still is, lacking in many countries.²⁹

Excess mortality also has the advantage of not only considering deaths directly caused by the virus but also those indirectly caused by the pandemic's impact on healthcare systems and economies.

Learn more about excess mortality here:

Excess mortality during the Coronavirus pandemic (COVID-19)

To estimate excess mortality, researchers use national mortality data from countries where data is available, as well as statistical models – which rely on data on COVID-19 testing rates, confirmed cases and deaths, population age structure, state policies, and more – for other countries.

The estimated death toll we show for COVID-19 – 27 million deaths by November 2023 – comes from The Economist. The main reasons why I am relying on The Economist's estimates are that they are continuously updated, and their methodology is well documented.

In contrast, while the World Health Organization (WHO) and the Institute for Health Metrics and Evaluation (IHME) have also estimated the number of excess deaths, their latest estimates were only based on the time period until the end of 2021. For this time period, all three sources provide similar estimates (18.2 million deaths were estimated by the IHME; 14.8 million deaths were estimated by the WHO; and 17.8 million deaths were estimated by The Economist).³⁰

The chart below shows the excess mortality during COVID-19, as estimated by The Economist, along with the number of confirmed deaths. As you can see, there is wide uncertainty around the total number of excess deaths during the pandemic. However, even the lowest estimates are much higher than the number of confirmed deaths – reflecting the limited amount of testing and death registration globally during the pandemic.

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Our articles and data visualizations rely on work from many different people and organizations. When citing this article, please also cite the underlying data sources. This article can be cited as:

Saloni Dattani (2023) - "What were the death tolls from pandemics in history?" Published online at OurWorldInData.org. Retrieved from: 'https://ourworldindata.org/historical-pandemics' [Online Resource]

BibTeX citation

@article{owid-historical-pandemics,      author = {Saloni Dattani},      title = {What were the death tolls from pandemics in history?},      journal = {Our World in Data},      year = {2023},      note = {https://ourworldindata.org/historical-pandemics}  }

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