Smallpox killed an estimated 300 to 500 million people in the 20th century alone, making it one of the deadliest diseases in human history. Over the full span of its existence, stretching back at least 3,000 years, the total death toll likely reaches into the billions. The disease was officially eradicated in 1980, the first and still only human disease to be wiped out entirely.
The 20th Century Death Toll
The most commonly cited figure is 300 to 500 million deaths during the 1900s. To put that in perspective, all wars and armed conflicts in the 20th century combined killed roughly 100 to 150 million people. Smallpox killed two to three times as many, even as vaccination campaigns were actively shrinking its reach throughout that century.
Before those campaigns took hold, smallpox killed roughly 2 million people per year worldwide. As late as 1967, the year the World Health Organization launched its intensified eradication program, the disease still infected 10 to 15 million people annually and killed about 2 million of them.
Why Smallpox Was So Deadly
Two strains of the virus circulated in human populations. The more common and dangerous strain, variola major, killed about 30% of the people it infected. The milder strain, variola minor, had a fatality rate of 1% or less. Most of the enormous death toll came from variola major.
The virus spread efficiently from person to person. In a population with no immunity, a single infected person would, on average, infect about 7 others, based on outbreak data published in the American Journal of Epidemiology. That transmission rate, combined with the 30% fatality rate, meant the virus could devastate entire communities in weeks. Survivors were often left blind or severely scarred.
The Destruction of Indigenous Populations
Some of the most catastrophic death tolls occurred in the Americas after European contact. Indigenous peoples had no prior exposure to smallpox and no immunity whatsoever. The results were staggering. In coastal New England, epidemics in the early 1600s killed as many as 90% of the native population in some areas. Between disease and war, the total regional native population dropped by roughly 90% in the first half of the 17th century.
In Mexico and Central America, recurring epidemics (smallpox chief among them, along with measles and typhus) reduced a population of 8 to 15 million in 1520 to just 1.5 million by 1650. On the island of Hispaniola, a precontact population of at least 60,000 declined to fewer than 2,000 by 1542. The historian Henry Dobyns estimated that 90% of the population of Mesoamerica and Andean South America had perished by 1568, less than 50 years after initial contact.
These numbers are difficult to state precisely because precontact population records don’t exist, and smallpox often arrived ahead of the Europeans themselves, carried along trade routes. But the scale of destruction is not seriously disputed. Smallpox reshaped the demographics of entire continents.
Historical Toll Before the Modern Era
Reaching further back, smallpox was a constant killer across Europe, Asia, and Africa for millennia. Evidence of the disease has been found on Egyptian mummies dating to the 3rd century BCE. In 18th-century Europe, smallpox killed an estimated 400,000 people per year and was the leading cause of blindness. About one in three Europeans who contracted the disease died from it, and nearly everyone was exposed at some point in their lives.
In Asia, the toll was similarly enormous. Smallpox epidemics swept repeatedly through China, India, and Japan over centuries. India alone accounted for a large share of global smallpox deaths well into the 20th century.
How Eradication Happened
Vaccination against smallpox began in 1796 when Edward Jenner demonstrated that exposure to cowpox provided immunity. Over the next 170 years, vaccination slowly reduced the disease’s reach, but it persisted in regions with limited public health infrastructure.
The WHO’s intensified eradication campaign, launched in 1967, used a strategy of surveillance and ring vaccination: finding every outbreak, then vaccinating everyone around it to cut off transmission. The last person to contract smallpox naturally was Ali Maow Maalin, a hospital cook in Somalia, who developed variola minor on October 22, 1977. He survived.
In May 1980, the 33rd World Health Assembly officially declared that “the world and all its peoples have won freedom from smallpox.” Routine vaccination ended worldwide shortly after. Today, the only known samples of the virus exist in two high-security laboratories: the CDC in Atlanta and the Russian State Centre for Research on Virology and Biotechnology in Koltsovo, Russia.
Adding Up the Total
No single number can capture the full toll of smallpox across human history. The 300 to 500 million figure covers only the 20th century. Adding the 18th and 19th centuries in Europe alone contributes tens of millions more. The collapse of indigenous populations in the Americas, while driven by multiple diseases, was dominated by smallpox and likely killed tens of millions. Centuries of epidemics across Asia and Africa add further to the count.
Reasonable estimates for the total death toll across all of recorded history range from 500 million to over 1 billion. By any measure, smallpox killed more people than any other single infectious disease. Its eradication remains one of the greatest achievements in the history of medicine.