Historians and epidemiologists have documented more than 20 major pandemics throughout recorded history, depending on how broadly you define the term. The World Health Organization defines a pandemic simply as “the worldwide spread of a new disease.” By that measure, the list includes ancient plagues, centuries of cholera waves, devastating flu outbreaks, and the viral pandemics of the modern era. Some, like HIV/AIDS, are still ongoing.
The number you land on depends on whether you count each cholera wave separately (there have been seven), whether you include diseases spread through colonization, and how widespread an outbreak needs to be before it qualifies. Here’s a walkthrough of the major ones, from earliest to most recent.
The Ancient and Medieval Plague Pandemics
The bacterium Yersinia pestis, which causes bubonic plague, is responsible for three distinct pandemics spanning roughly 1,500 years.
The first was the Justinianic Plague, which struck the Byzantine Empire in 541 CE and recurred in waves until around 549 CE. Infected individuals faced a 60 to 80 percent chance of dying. The outbreak devastated Mediterranean port cities and reshaped the political landscape of late antiquity.
The second plague pandemic is the one most people know: the Black Death, which swept through Europe from 1346 to 1353. It killed roughly 50 million people, wiping out an estimated 50 to 60 percent of Europe’s population in just six years. Smaller plague outbreaks continued to flare across Europe for centuries afterward.
The third plague pandemic began in the 1890s and lasted until around 1940, mainly affecting communities in Asia and Africa. It was less catastrophic in terms of total death toll than its predecessors but still killed millions and prompted major advances in understanding how the disease spread.
Diseases of the Columbian Exchange
After 1492, European contact with the Americas introduced smallpox, measles, and other infectious diseases to populations with no prior immunity. The result was catastrophic: an estimated 48 million deaths, calculated as the net population reduction compared to pre-contact numbers. Some Indigenous communities lost 90 percent or more of their people within a few generations.
Smallpox alone was fatal in up to 30 percent of cases. It continued to kill on a massive scale worldwide for centuries until the WHO declared it eradicated in 1980, making it the only infectious disease ever fully eliminated through human effort.
Seven Cholera Pandemics Since 1817
Cholera, caused by the bacterium Vibrio cholerae, has produced seven recognized pandemics since 1817. Each wave originated in South Asia and spread outward along trade routes and migration paths. The sixth pandemic lasted from 1899 to 1923. The seventh began in Indonesia in 1961 and continues to this day, with over 900,000 recorded deaths globally.
If you count each cholera pandemic individually, they alone add seven entries to the historical total. Some tallies group them together as one ongoing problem, which is part of why different sources give different numbers when answering “how many pandemics have there been.”
The 1889 Russian Flu
Before the more famous 1918 pandemic, a severe respiratory illness swept the globe starting in 1889. Known as the Russian flu, it killed an estimated 4 million people. Its exact cause is still debated. Some researchers believe it was an influenza virus, while others have suggested it may have been caused by a coronavirus. It was one of the first pandemics to spread rapidly along railroad and steamship networks, giving the world a preview of how modern transportation could accelerate disease transmission.
The 1918 Influenza Pandemic
The 1918 pandemic remains the deadliest outbreak of the modern era. Caused by an H1N1 influenza virus, it killed an estimated 50 million people worldwide, with some estimates reaching as high as 100 million. The CDC has called it “the mother of all pandemics.”
What made it uniquely dangerous was its tendency to kill otherwise healthy young adults, not just the elderly and very young. It spread in three distinct waves between 1918 and 1919, with the second wave being by far the most lethal. Every influenza A pandemic since then has been caused by descendants of the 1918 virus, including reassorted strains that emerged in later decades.
The Mid-Century Flu Pandemics
Two more influenza pandemics followed in the 20th century. The 1957 Asian flu killed approximately 2 million people worldwide, and the 1968 Hong Kong flu killed another 2 million. Both were caused by new influenza strains that had enough genetic novelty to evade existing immunity in most of the population. While serious, neither approached the scale of 1918, partly because antibiotics could treat secondary bacterial infections and public health infrastructure had improved.
HIV/AIDS: A Pandemic Still Underway
HIV/AIDS is sometimes left off pandemic lists because it doesn’t spread through respiratory droplets and its timeline is measured in decades rather than years. But by any epidemiological standard, it qualifies. Since the virus was first identified in 1981, it has claimed 44.1 million lives globally. In 2024 alone, 1.3 million people newly acquired HIV.
Unlike most pandemics on this list, HIV/AIDS has no natural endpoint. Antiretroviral therapy has transformed it from a death sentence into a manageable chronic condition for those with access to treatment, but the pandemic is far from over, particularly in sub-Saharan Africa and other regions with limited healthcare infrastructure.
The 2009 Swine Flu
The 2009 H1N1 pandemic (swine flu) was the first influenza pandemic of the 21st century. It turned out to be far milder than initially feared. The CDC estimated that in the United States alone there were about 60.8 million cases, 274,000 hospitalizations, and 12,469 deaths during the first year. Globally, the estimated death toll ranged from roughly 152,000 to 575,000, representing between 0.001 and 0.007 percent of the world’s population. By comparison, seasonal flu kills 290,000 to 650,000 people in a typical year, which is why some have questioned whether the 2009 outbreak warranted the pandemic label, even though it technically met the criteria.
COVID-19
The most recent pandemic began in early 2020 when a novel coronavirus, SARS-CoV-2, spread rapidly from China to every inhabited continent. Official death counts, which rely on confirmed cases reported to the WHO, substantially undercount the true toll. Excess mortality analysis, which compares total deaths to expected baselines, estimates around 27 million excess deaths through November 2023. The WHO ended its requirement for daily case reporting in August 2023, marking a transition from emergency response to long-term surveillance.
Are Pandemics Becoming More Frequent?
It can feel that way. The 20th and 21st centuries have seen at least six pandemic-level events (1918 flu, 1957 flu, 1968 flu, HIV, 2009 flu, COVID-19), compared to longer gaps between major outbreaks in earlier centuries. Urbanization, international air travel, deforestation, and closer human contact with animal populations all create more opportunities for new pathogens to emerge and spread.
That said, a 2021 study published in the Proceedings of the National Academy of Sciences offered some nuance. The researchers estimated that when the 1918 pandemic occurred, a flu outbreak of that intensity had a mean recurrence time of about 181 years. Using data from 2000 to 2019, they calculated the recurrence time for a similarly devastating pandemic at 877 years. In other words, smaller pandemics have become more frequent, but a repeat of something on the scale of 1918 remains statistically rare in any given lifetime.
So the total count of major pandemics in recorded history lands somewhere between 15 and 25, depending on your definitions. The core list, the events virtually every epidemiologist would include, numbers around a dozen: three plague pandemics, seven cholera pandemics, the 1918 flu, HIV/AIDS, and COVID-19, with the Columbian Exchange diseases and several smaller flu pandemics filling out the picture.