The Eradication of Smallpox
Vaccination, Ring Containment, and the Last Natural Case
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This audiobook traces smallpox from its ancient history through the development of variolation and Edward Jenner's cowpox vaccine. It covers the World Health Organization's Intensified Eradication Programme, including Donald Henderson's leadership and the controversial ring vaccination strategy that stopped outbreaks by isolating infected areas.
The book also examines the 1978 laboratory accident in Birmingham that killed a woman, the 1980 WHO declaration of eradication, and ongoing debates about whether to destroy remaining smallpox stocks. Medical historians, public health professionals, and anyone interested in how humanity conquered its deadliest disease will find this essential listening.
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Overview
Smallpox shaped human history for thousands of years, with evidence suggesting the virus appeared 3,000 to 4,000 years ago. Reliable written records date back to around 500–1000 CE, though physical signs have been found in Egyptian mummies from about 3,000 years ago. The disease had a devastating impact, especially on populations in the Americas and Australia who had no immunity. In the 18th century, it killed around 400,000 Europeans yearly, including five monarchs, and caused blindness in one-third of survivors. Between 20 and 60% of infected people died, with over 80% of children losing their lives. By the 20th century, hundreds of millions had died from smallpox, with 50 million cases reported globally in the early 1950s. In 1967, the WHO said 15 million got sick and two million died. After widespread vaccination efforts, the World Health Organization certified global eradication in May 1980. Smallpox is one of only two infectious diseases ever fully eradicated—rinderpest being the other.
Eurasian epidemics
Smallpox left its mark across Eurasia for centuries, with historians suggesting it may have fueled the Plague of Athens in 430 BCE and the Antonine Plague in 165–180 CE, which killed up to one-third of the Roman population. The disease spread along trade routes, reaching Japan by 735–737 and the Philippines by the 4th century. In India, the Sushruta Samhita described smallpox in the 4th century, linking it to a goddess named Sitala. By 581 AD, Bishop Gregory of Tours gave the first clear Western account of the disease. The Persian physician Muhammad ibn Zakariya ar-Razi, known as Rhazes, distinguished smallpox from measles in the 9th century. In the 18th century, it killed hundreds of thousands across Europe and India, with one in seven Russian children dying before their first birthday. A Franco-Prussian War outbreak in 1870–1875 claimed 500,000 lives, prompting stricter vaccination laws in some countries.
African epidemics
Smallpox reached Africa before written records, with early encounters linked to an elephant war around 568 CE when Ethiopian troops returning from Mecca carried the disease. Arab ports likely imported smallpox as early as the 13th century, though clear evidence appears in the 16th century. As tribes invaded coastal towns, deadly epidemics struck local populations while sparing Portuguese settlers. Caravan routes connecting populated areas to Nubia and Ethiopia probably spread the disease since the 11th century, but written accounts emerged with the slave trade. Enslavement expeditions pushed smallpox inland along these paths, infecting those waiting or traveling on ships. In Angola, smallpox arrived shortly after Portuguese settlement in 1484; a 1864 outbreak killed 25,000 people, one-third of the local population. A ship from India brought smallpox to Cape Town in 1713, devastating both European settlers and the Khoisan people. Two more outbreaks followed in 1755 and 1767, wiping out entire clans. By 1840, smallpox again struck Cape Town, killing 2,500, and later spread to Uganda. The Griqua tribe lost up to eighty percent of its population in 1831, while tribes in Kenya were decimated through 1899. Along the Zaire river basin, entire areas became uninhabitable after epidemics. In Ethiopia and Sudan, six major outbreaks occurred during the 19th century: 1811–1813, 1838–1839, 1865–1866, 1878–1879, 1885–1887, and 1889–1890.
Epidemics in the Americas
Smallpox devastated the Americas after European contact, killing up to 95% of native populations. In 1519, Hernán Cortés arrived in Mexico, where smallpox from Hispaniola spread rapidly, weakening the Aztec Empire. The disease killed most of the Aztec army and 25% of the population, leaving the empire vulnerable when Cortés returned in 1521. Similarly, in the Inca Empire, smallpox struck before Spanish arrival, killing leaders and causing internal war. By 1561, it reached Chile, killing 20 to 25% of the native people. In Massachusetts, outbreaks hit Native Americans from 1633 onward, with Boston seeing six epidemics between 1636 and 1698. During the siege of Fort Pitt in 1763, British forces allegedly gave blankets infected with smallpox to Delaware delegates, though the effectiveness remains uncertain. Smallpox continued killing thousands during the American Revolutionary War in the 1770s.
Australia
Smallpox arrived in Australia in the 18th century, with the first outbreak recorded in April 1789, about sixteen months after the First Fleet arrived. Governor Arthur Phillip said half the Aboriginal people living around Sydney Cove died during the outbreak, although later estimates, like those of Professors Carmody and Hunter, put the figure at around thirty percent. There is an ongoing debate over how it entered the continent—whether through British settlers or Makassan mariners. Dr J. H. L. Cumpston suggested the British, a view reiterated by Noel Butlin and David Day, who proposed smallpox was used as a biological weapon. However, historian Judy Campbell argued in Invisible Invaders that the disease likely didn't arrive via the First Fleet, citing the unlikelihood of variolous matter surviving the voyage. She supported her claim with input from Frank Fenner, who had worked on global smallpox eradication. Campbell's theory was challenged by Christopher Warren and Craig Mear, who maintained the British supply could have carried the virus. Others, like John Connor and H. A. Willis, weighed in, with Willis endorsing Campbell's argument after reviewing Fenner's WHO report. The Makassan theory gained traction through Campbell and C. C. Macknight, but Michael Bennett and others pointed out inconsistencies, including lack of trade routes and Aboriginal oral traditions. A third idea, proposed by Dr G. E. Ford and supported by Curson, Wright, and Hunter, suggests the outbreak was chickenpox, not smallpox, though Mark Wenitong and John Maynard argue strongly for smallpox. Another major outbreak occurred in 1828–1830 near Bathurst.
Polynesia
Smallpox devastated indigenous populations across the Pacific, including Polynesians. In New Zealand, by 1840, a ship carrying the disease was successfully quarantined, stopping an epidemic among the Māori. The only major outbreak in New Zealand occurred in 1913, affecting Māori in northern regions. That same year, the Rapa Nui people of Easter Island were nearly wiped out by smallpox, according to Te Rangi Hiroa, who reported this to a medical congress in Melbourne in 1914.
Micronesia
In February 1854, a whaler named the Delta brought smallpox to Pohnpei, a Micronesian island. The people there first tried to appease their spirits with feasting before hiding from the disease. The illness killed more than half the population. Chiefs died, which threw society into chaos. Some blamed the God of Christian missionaries. The missionaries saw the outbreak as divine punishment and offered inoculations, though they often kept the treatment from the priests. The epidemic ended in October 1854.
Eradication
Long before modern medicine, people noticed that those who survived smallpox once were immune to it again. In China, by the 10th century, a method called variolation was developed, where matter from smallpox sores was deliberately introduced into the skin to produce a milder infection. This practice spread across different regions with varying techniques. It remained the primary way to prevent smallpox until Edward Jenner's breakthrough in 1796, when he discovered that cowpox could protect against smallpox. Vaccination based on this idea followed for many years after. The disease has been eradicated since 1979.
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Overview
Smallpox was an infectious disease caused by the variola virus, the last case diagnosed in October 1977, with global eradication certified by the World Health Organization in 1980. Initial symptoms included fever and vomiting, followed by mouth ulcers and a skin rash that developed into fluid-filled blisters, which scabbed over and left scars. The disease spread mainly through face-to-face contact or contaminated objects, with a 30% death rate, higher among infants. Prevention came through vaccination, and although antiviral treatments existed after eradication, they were not available during the outbreak. The earliest evidence dates to around 1500 BCE in Egyptian mummies, and it killed up to 500 million people in the last 100 years of its existence. Inoculation began in China around the 1500s, adopted in Europe by the 18th century. Edward Jenner introduced the modern vaccine in 1796, and in 1967, the WHO intensified efforts to eliminate it. The term "smallpox" first appeared in England in the 16th century, distinguishing it from syphilis, also known as the "great pox." Other historical names included pox, speckled monster, and red plague. Smallpox is one of only two infectious diseases ever eradicated, the other being rinderpest in 2011.
Classification
There are two main forms of smallpox: variola major, which is the more severe and common type, causing a widespread rash and high fever, and variola minor, a rarer form that leads to less serious illness with a discrete rash and historically low death rates of around 1% or less. Subclinical infections, where people show no symptoms, were also observed but not frequent. Another variation, called variola sine eruptione, occurs mainly in vaccinated individuals and presents only with fever after the typical incubation period, identifiable only through antibody tests or very rarely via viral culture. Additionally, two extremely rare and deadly forms existed: the malignant (flat) and hemorrhagic types, both usually fatal.
Ordinary
Among unvaccinated people, at least 90% of smallpox cases followed the ordinary type. By the second day of the rash, macules had become raised papules. The third or fourth day brought vesicles as the papules filled with opalescent fluid. Within 24 to 48 hours, that fluid turned opaque and turbid, forming pustules. By the sixth or seventh day, all lesions were pustules. Between seven and ten days, they matured and reached maximum size—sharp, round, tense, and firm to the touch, deeply embedded in the dermis like small beads. Fluid slowly leaked from them, and by the end of the second week, the pustules began to deflate and dry up, forming crusts or scabs. By day 16 to 20, scabs covered all lesions, starting to flake off and leave depigmented scars. The rash was discrete, with pustules standing out separately on the skin. It was densest on the face, denser on the extremities than the trunk, especially on the distal parts of the limbs, and involved the palms and soles in most cases.
Confluent
When the blisters came together, they formed a continuous rash that peeled away the top layer of skin. People suffering from this severe form of smallpox often stayed sick even after scabs had covered every sore. One group of cases showed that more than sixty percent of those with confluent smallpox died from it.
Modified
Modified smallpox appeared mostly in people who had been vaccinated before, and was very rare in those who hadn’t. One case study showed that only 1–2% of modified cases occurred in unvaccinated individuals, compared to around 25% in vaccinated people. The early symptoms still happened, but might have been milder than in regular smallpox. There was usually no fever as the rash developed. The sores were fewer, came on faster, and were more shallow. They often didn’t look exactly like typical smallpox. This version of variola major was rarely fatal. Because of these differences, it could easily be mistaken for chickenpox.
Malignant
Malignant smallpox, also known as flat smallpox, was a severe and nearly always fatal form of the disease. Unlike ordinary smallpox, the lesions remained almost flat with the skin even as they matured. It accounted for five to ten percent of cases historically, most of which were children. The illness began with a long, intense prodromal phase including high fever and serious symptoms of viremia that lasted even after the rash appeared. The rash on mucous membranes was widespread, and skin lesions developed slowly, becoming flat by the seventh or eighth day, as if buried in the skin. These vesicles contained little fluid, felt soft and velvety, and sometimes had hemorrhages. Death usually came between the eighth and twelfth day, often preceded by a gray coloration of the lesions and abdominal swelling. This form is thought to be linked to weak cell-mediated immunity. If someone survived, the lesions faded without scarring.
Hemorrhagic
Hemorrhagic smallpox is a severe and rare form of the disease, occurring in about 2 percent of infections, mostly in adults. It's marked by extensive internal bleeding into the skin, mucous membranes, and organs, giving the appearance of charred or blackened flesh—this is why it’s also known as variola nigra or "black pox." Unlike typical smallpox, pustules usually don’t form in hemorrhagic cases. This form has very rarely been caused by the variola minor virus. While bleeding may occur in milder cases without affecting survival, hemorrhagic smallpox is generally fatal. Vaccination does not seem to offer protection against it, and some individuals who were recently revaccinated still developed the disease. It has two distinct forms.
Early
The early or fulminant form of hemorrhagic smallpox, known as purpura variolosa, starts with sudden high fever, severe headache, and abdominal pain. The skin turns dusky and red, quickly followed by bleeding under the skin, in the eyes, and mucous membranes. Death often comes suddenly between the fifth and seventh days of illness, even before visible spots appear. Some survivors live a few more days, during which skin peels and fluid builds up beneath it, breaking easily. Those who die are usually conscious until the end. At autopsy, doctors found petechiae and bleeding in the spleen, kidneys, liver, heart, and other organs. This form was often misdiagnosed while alive, with correct identification only happening after death. It occurred more frequently in pregnant women—about 16% of unvaccinated pregnant cases were this early hemorrhagic type, compared to around 1% in nonpregnant women and men. The fatality rate approached 100%.
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Overview
The smallpox vaccine prevents infection caused by the variola virus and was the first vaccine created for a contagious disease. In 1796, British physician Edward Jenner proved that exposure to cowpox gave immunity to smallpox; cowpox acted as a natural vaccine until modern versions were developed in the twentieth century. From 1958 to 1977, the World Health Organization conducted a global effort that led to the eradication of smallpox, making it the only human disease ever eliminated. Though routine vaccination no longer takes place, the vaccine is still manufactured for research and protection against bioterrorism. The term "vaccine" comes from vacca, the Latin word for cow, reflecting Jenner's use of cowpox, which he referred to as variolae vaccinae. In 1939, Allan Watt Downie demonstrated that the modern vaccine was serologically different from cowpox, establishing vaccinia as a separate viral species. Whole-genome sequencing has shown that vaccinia is most closely related to horsepox, while cowpox strains found in Great Britain are the least related. The smallpox vaccine also helps prevent infections caused by similar orthopoxviruses such as Mpox, with three approved vaccines—MVA-BN, LC16m8, and ACAM2000—listed by the WHO as essential medicines.
Types
The smallpox vaccine is the oldest vaccine, evolving through three distinct generations over nearly two centuries. From 1796 to the 1880s, it was passed from person to person through arm-to-arm vaccination. By the 1840s, it began being grown in cattle, and by the 1880s, calf lymph vaccine had become the standard. First-generation vaccines, grown on live animal skin, were widely used from the 1950s through the 1970s to help eradicate smallpox. Second-generation vaccines, made in chorioallantoic membrane or cell cultures, offered greater purity and were used during the eradication campaign. Third-generation vaccines used attenuated vaccinia strains and saw limited use before eradication. All three generations remain in stockpiles today, though first and second are riskier, with serious side effects in about 1 to 10 per million vaccinations. Second and third-generation vaccines are still being produced, especially since the 2000s due to bioterrorism concerns.
First-generation
First-generation smallpox vaccines used live vaccinia virus grown in animal skin, mostly on cows, but also sheep. These vaccines were made into freeze-dried versions like Dryvax starting in the 1950s, allowing long-term storage without refrigeration. Vaccination involved multiple skin punctures with a bifurcated needle, cleaning the area with water rather than alcohol to avoid killing the virus. A successful vaccine reaction, called a "take," created a pus-filled lesion that crusts and leaves a scar. About one-third of people had side effects serious enough to affect daily life, and 15–20% developed fevers over 102°F. The vaccine could spread infection, with rare but severe complications like encephalitis or myopericarditis. Predictive models from 2006 estimated deaths from uncontrolled infection in Germany and the Netherlands if mass vaccination occurred using strains such as New York City Board of Health, Lister, or Bern.
Second-generation
Second-generation smallpox vaccines used live vaccinia virus grown in chicken eggs or cell cultures, rather than on animal skin like first-generation versions. In 1932, Ernest William Goodpasture and colleagues grew the virus on chorioallantoic membranes of chicken embryos. The Texas Department of Health began using egg-based vaccine in 1948, and Lederle Laboratories sold its Avianized version in 1959. The World Health Organization supported cell culture work in the 1960s at the Dutch RIVM, testing a vaccine from the Lister/Elstree strain in Indonesia in 1973. Later, in the 2000s, two new cell culture vaccines were made from the same strain: Elstree-BN and VV Lister CEP. ACAM2000, developed by Acambis and later sold to Emergent Biosolutions, was approved for mpox prevention in the U.S. in 2024.
MVA
Modified vaccinia Ankara, known as MVA, began as a strain originally maintained in Ankara, Turkey, on donkeys and cows. In 1953, it was transported to West Germany, where Herrlich and Mayr cultivated it at LMU Munich using chorioallantoic membrane. After 572 serial passages, the virus had lost more than 14 percent of its genetic material and became unable to reproduce in human cells. MVA was used in West Germany between 1977 and 1980, but only 120,000 doses were administered before smallpox eradication ended the vaccination effort. It produced fewer antibodies than traditional vaccines. Japan evaluated MVA and decided against it due to its weak immune response, opting instead to develop their own attenuated version. In the 2000s, researchers tested MVA in animal models at much higher dosages, discovering that when given to monkeys at 40 times the amount used in Dryvax, it generated a quicker immune reaction while still causing fewer side effects.
MVA-BN
MVA-BN, known as Imvanex in Europe, Imvamune in Canada, and Jynneos in the U.S., is a smallpox vaccine produced by Bavarian Nordic using cell culture to grow the virus. It's given as a subcutaneous injection and does not produce the typical skin reaction called a “take.” The vaccine can also be given intradermally to increase available doses, making it suitable for immunocompromised individuals or those at risk from vaccinia infection. It’s been approved for use in the European Union, Canada, and the United States, and clinical trials show it's just as effective as ACAM2000 but safer. In September 2024, the WHO prequalified it for both smallpox and mpox.
LC16m8
LC16m8 is a weakened vaccinia virus developed in Japan by So Hashizume at the Chiba Serum Institute. He repeatedly passed the Lister strain through rabbit kidney cells, halting at specific points to cultivate clones on chorioallantoic membrane and select for pock size. This created LC16m8, a variant with all original vaccinia genes but a single-nucleotide deletion in the B5R membrane protein limiting extracellular enveloped virus production. Animal studies show antibodies against other membrane proteins still offer immunity. Approved in Japan in 1975 after testing on over 50,000 children, it produces vaccine "take" with MVA-like safety. In November 2024, WHO added LC16m8 to its Emergency Use Listing based on updated safety data, confirming effectiveness—including in people with well-controlled HIV. It is commercially known as LC16 KMB.
Safety
The smallpox vaccine vaccinia is effective because it's infectious, but can cause serious problems for people with weak immune systems—like those undergoing chemotherapy or living with AIDS, individuals with a history of eczema, pregnant women, or organ transplant recipients. It's also not recommended for anyone who lives with someone in one of these high-risk groups. According to the US Centers for Disease Control and Prevention, if you're exposed to the virus, getting vaccinated within three days might prevent illness or reduce its severity. If given between four and seven days after exposure, it still offers some protection. In May 2007, the Vaccines and Related Biological Products Advisory Committee of the FDA voted unanimously that a new vaccine made by Acambis, called ACAM2000, was both safe and effective for people at high risk of exposure. However, due to its serious side effects, it's only available through the CDC's Strategic National Stockpile. The vaccine was approved for use in the United States in August 2007. Third-generation vaccines like LC16, which replicates poorly, or MVA, which doesn't replicate at all, are safer. LC16 has been shown to be safe in people with well-controlled HIV but hasn't been tested in immunocompromised individuals. MVA is considered safe for those with weakened immune systems by the US CDC.
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Overview
Donald Ainslie Henderson was an American physician, educator, and epidemiologist who led a ten-year global effort from 1967 to 1977 to eradicate smallpox, launching international childhood vaccination programs in the process. From 1977 to 1990, he served as Dean of the Johns Hopkins School of Public Health. Later in his career, he helped establish national programs for public health preparedness and response to biological attacks and disasters by founding the Center for Health Security. At the time of his death in 2016, Henderson held the titles of Professor and Dean Emeritus at the Johns Hopkins Bloomberg School of Public Health, as well as Professor of Medicine and Public Health at the University of Pittsburgh, and was a Distinguished Scholar and former Founder of the Center for Health Security.
Early life and education
Donald Henderson came into the world in Ohio, the son of an engineer named David and a nurse named Eleanor McMillan. His path toward medicine was shaped by his Canadian uncle, William McMillan, who practiced as a general practitioner and also served in the Canadian House of Commons. Henderson earned his medical degree from the University of Rochester School of Medicine in 1954 after first graduating from Oberlin College in 1950. He completed his residency at Mary Imogene Bassett Hospital in Cooperstown, New York, and later joined the Epidemic Intelligence Service as a Public Health Service Officer at the Communicable Disease Center—now known as the Centers for Disease Control and Prevention. In 1960, he received his MPH from the Johns Hopkins School of Hygiene and Public Health, which is now called the Johns Hopkins Bloomberg School of Public Health.
Eradication of smallpox
Donald Henderson led a major effort to eliminate smallpox, starting with a USAID program in 1967 that targeted 18 African countries. He later became director of the World Health Organization’s global campaign in 1966, when smallpox was widespread in Brazil, Africa, and South Asia, causing over 10 million cases and 2 million deaths yearly. The strategy relied on surveillance and containment, quickly reporting cases and vaccinating contacts. Henderson worked with staff from 73 countries to track and stop the disease. The final case was recorded in Somalia on October 26, 1977. Three years later, the World Health Assembly said smallpox vaccination could stop. This made history as the first human disease ever eradicated. The success led to WHO’s Expanded Program on Immunization, which targeted other diseases like polio and measles.
Later work
After helping eradicate smallpox, Donald Henderson became Dean of the Johns Hopkins School of Public Health from 1977 through August 1990. He received the National Medal of Science in 1986 from Ronald Reagan for his leadership of the WHO campaign and worked to reverse Reagan's decision to stop paying WHO. In 1991, he joined the White House as associate director for life sciences at the Office of Science and Technology Policy, then served in the Department of Health and Human Services in two roles: deputy assistant secretary and senior science advisor. In 1998, he founded the Johns Hopkins Center for Civilian Biodefense Strategies, now called the Johns Hopkins Center for Health Security. Following the September 11 attacks, Henderson led the Office of Public Health Preparedness, later renamed the Office of the Assistant Secretary for Preparedness and Response, with a $3 billion budget from Congress. In 2006, he co-authored a paper skeptical of social distancing during pandemics, saying such measures could cause serious economic and social harm without clear evidence of effectiveness. At his death, Henderson was Editor Emeritus of the journal Health Security.
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Overview
Mathematical models help scientists understand how infectious diseases spread and what might happen during an outbreak. These models use assumptions and real data to figure out key details about how diseases move through populations. By plugging in information about infection rates, recovery times, and other factors, researchers can predict the likely course of an epidemic. The models also show how different actions—like mass vaccination campaigns—might change the outcome. This helps public health officials choose which strategies to try or avoid. They can even forecast future trends, guiding decisions about when and where to apply interventions. Such tools were essential in planning the global effort to eliminate smallpox.
History
The idea of using math to understand how diseases spread began with John Graunt in 1662, when he studied weekly death records and set the stage for what is now known as the "theory of competing risks." A major step forward came in 1760 when Daniel Bernoulli used mathematical calculations to support smallpox inoculation, showing it could raise life expectancy from about 26 years to nearly 29. In the early 1900s, scientists began applying the law of mass action to better explain epidemic patterns. By the 1920s, models like the Kermack–McKendrick model from 1927 and the Reed–Frost model from 1928 helped describe how people move between being susceptible, infected, or immune. More recently, agent-based models have offered more detailed simulations, helping guide public health decisions during events like the SARS-CoV-2 pandemic.
Assumptions
Mathematical models rely heavily on assumptions, and their accuracy depends entirely on those starting points. When predictions don't match reality—and the math is sound—the original ideas must shift to reflect reality better. One such assumption is a rectangular and stationary age distribution, where everyone in the population reaches the same age L and then dies, with equal numbers of people at each age level up to L. This works well in developed countries with low infant death rates and high life expectancy. Another key idea is that individuals mix homogeneously, meaning they interact randomly across the whole group rather than clustering within smaller communities. That's rarely true, since people often stay within their own groups—like Londoners mixing mostly with other Londoners, or teenagers with other teens, or ethnic communities such as the Turkish population in the city. Still, assuming random mixing keeps the math simple and manageable.
Stochastic
A stochastic model is a method used to predict possible results by incorporating random changes over time. These models are built on the idea that risk, exposure, and disease spread involve chance variations. They help estimate how illnesses might move through populations, whether small or large. At their core, they rely on statistical techniques that look at individual behaviors and outcomes. This approach allows scientists to better understand uncertainty in health dynamics. Such tools are essential when studying how diseases behave in real-world settings. Stochastic methods offer a way to study disease dissemination at the level of agents within a population. In this way, they provide insight into the unpredictable nature of infection patterns.
Deterministic
When studying diseases that spread through large groups of people, like tuberculosis, scientists use deterministic or compartmental models to track how the illness moves through a population. These models divide the population into different subgroups, each representing a stage of infection. The changes from one group to another are shown using differential equations, which describe how quantities change over time. For these models to work, it's assumed that the number of people in each group can be measured continuously and that the process follows a clear, predictable path. In other words, the future state of the system depends only on its past, as defined by the model itself.
Kinetic and mean-field
These models are classified as deterministic, but they bring in complex social details like how much people interact, what they believe, their wealth, and where they live—factors that deeply shape how a disease spreads. Instead of using ordinary differential equations like older models do, they use partial differential equations to capture this complexity. They’re built on the principles of kinetic theory, starting with individual interactions between agents, and offer a more precise picture of how epidemics unfold.
Sub-exponential growth
A common way to understand how epidemics spread is to imagine that one person infects two others, who then each infect two more, and so on, with the number of cases doubling at each step. It’s like a game of tag where the tagged players chase those who haven’t been tagged yet, and the game gets more chaotic as it goes on. This kind of growth leads to a steep curve that rises quickly and then plummets once everyone has been infected—there's no gradual peak or slowdown, no herd immunity to slow things down. That’s not what we see in real life, though. In reality, epidemics follow a different pattern, one that includes a peak and a slower decline.
Epidemic Models on Networks
Epidemics spread through networks of human contact, and scientists model this using graphs where each person is a node and connections between them are links. These contact networks help map how diseases move, but to understand transmission, we also need the transmission network — which shows exactly how the disease spreads from person to person. When the transmission network looks like a tree locally, the basic reproduction number R₀ can be calculated using the average degree and the second moment of the degree distribution. In simpler cases, such as when contacts follow a Poisson distribution, R₀ equals the product of the transmission rate β, the recovery rate γ, and the mean degree ⟨k⟩. This mathematical approach helps guide strategies like vaccination and containment during outbreaks.
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Overview
Eradicating infectious diseases means stopping their global spread until none remain. Only two have been fully eliminated: smallpox in humans and rinderpest in animals. Removing diseases requires strict conditions—clear understanding of how a pathogen spreads, effective tools like vaccines to block transmission, and no hidden reservoirs outside human populations. Rinderpest was eradicated because its infection source was easily identified in livestock. Measles research introduced critical community size theory, helping determine when diseases can no longer survive in populations. Vaccination before eradication efforts reduces carriers and spreaders. Accurate diagnosis is essential. Political support, funding, and public commitment play major roles. The process demands biological knowledge and technical readiness to make elimination possible.
Smallpox
Smallpox is the first and only infectious disease in human history to be completely wiped out through deliberate action. In 1798, Edward Jenner demonstrated that inoculation with material from cowpox sores provided protection. The disease came in two forms: variola major, which killed up to forty percent of those infected, and variola minor, also called alastrim, with a mortality rate under one percent. The final case of variola major was recorded in October 1975 in Bangladesh. The last known naturally occurring case of smallpox, variola minor, was found on 26 October 1977 in Ali Maow Maalin, Somalia. That case originated from an outbreak in the nearby district of Kurtunwarey, and all 211 contacts were traced, revaccinated, and closely watched. After two years of reviewing national records, an international commission declared global eradication on 9 December 1979, and the World Health Organization officially recognized that decision on 8 May 1980. Today, debate continues over whether labs in the US and Russia should keep the virus, since its release could spark new outbreaks among people born after the late 1980s, when routine vaccinations stopped.
Rinderpest
In the twentieth century, a series of efforts tried to eliminate rinderpest, a virus that affected cattle and other cloven-hoofed animals and is related to measles. These initiatives relied heavily on a live attenuated vaccine. The final campaign was successful under the direction of the Food and Agriculture Organization of the United Nations. After nine years with no reported cases, the FAO declared on 14 October 2010 that rinderpest had been completely eradicated. This made it the first and only disease affecting livestock to be eliminated through human action.
Poliomyelitis (polio)
A major drop in polio cases came after a vaccine was developed in the 1950s, and by 1960, Czechoslovakia became the first country certified as polio-free. In 1988, the World Health Organization, Rotary International, UNICEF, and the CDC launched the Global Polio Eradication Initiative with a goal to wipe out polio by 2000. The plan focused on routine and supplemental immunizations and outbreak surveillance. By 2021, only six cases were reported globally. The Americas, Western Pacific including China, Europe, Southeast Asia including India, and Africa have all been declared polio-free. Wild poliovirus type 2 was eradicated worldwide by 2015, followed by type 3 in 2019. Only Pakistan and Afghanistan still see transmission of wild poliovirus type 1.
Dracunculiasis
Dracunculiasis, or Guinea worm disease, is a painful parasitic illness caused by the nematode Dracunculus medinensis, spread through drinking water contaminated with copepods carrying the larvae. The Carter Center has led global eradication efforts alongside the CDC, WHO, UNICEF, and the Bill and Melinda Gates Foundation, with the goal of becoming the first parasitic disease ever eliminated. Unlike smallpox or polio, there is no vaccine or medicine for Guinea worm; instead, strategies focus on safer water supplies, infection containment, and education. These efforts reduced cases from over 100,000 in 1995 to just ten in 2025. As of 2025, 200 countries have been certified free of the disease, leaving only six—South Sudan, Ethiopia, Mali, Angola, Cameroon, and Chad—still affected. The final push is proving difficult because the worm now infects dogs, cats, and baboons, creating animal reservoirs that complicate eradication. The WHO still aims to eliminate the disease by 2030.
Yaws
Yaws is a disfiguring disease caused by the bacterium Treponema pallidum pertenue, closely related to the syphilis germ, and spread through direct skin contact. From 1952 to 1964, the Global Control of Treponematoses programme reduced global cases from about fifty million to two point five million. Though the program ended, yaws persisted in parts of Asia, Africa, and the Americas. In 2012, the WHO set a goal to eradicate it by 2020, which was missed, with a new target of 2030. A key development came when oral azithromycin was found effective; on Lihir Island between 2013 and 2014, a single dose reduced prevalence from 2.4% to 0.3% at twelve months. As of 2024, 16 countries were known to be endemic for yaws, with 152,164 suspected cases reported and 996 confirmed. Evidence of antibiotic resistance emerged in 2020, along with signs that the bacterium can infect primates, complicating eradication efforts.
Malaria
Malaria has been eliminated in parts of Europe, North America, Australia, North Africa, the Caribbean, and some regions of South America, Asia, and Southern Africa, with countries needing to show no local transmission for three years to be declared free of the disease. The WHO launched its Global Malaria Eradication Program in 1955, which was later suspended in 1969, but support picked up again after 2000. Though some global health leaders questioned whether eradication goals were realistic, the WHO reported a 60% drop in malaria deaths between 2000 and 2015. Their target was a further 90% reduction by 2030, with 40% reduction and elimination in 10 countries by 2020—though that goal was missed. Between 2000 and June 30, 2021, twelve countries were certified malaria-free, including Argentina, Algeria, El Salvador, and China. While Southeast Asia was on track for its 2020 goals, Africa and other regions fell behind. The Greater Mekong Subregion aims to eliminate malaria by 2025 and all malaria by 2030, having reduced cases significantly since 2000. The WHO also named 25 countries it is working with to reach elimination by 2025 under its E-2025 initiative.
Lymphatic filariasis
Lymphatic filariasis is a disease caused by mosquito-borne worms that can lead to elephantiasis. To stop transmission, annual mass distribution of combined oral medicines like albendazole with either ivermectin or diethylcarbamazine has proven effective. In sub-Saharan Africa, this approach uses albendazole and ivermectin, while other regions use albendazole and diethylcarbamazine. The strategy aims to eliminate microfilariae in the blood and reduce mosquito-borne spread, especially when combined with measures like insecticide-treated bed nets. The Americas bear most of the burden, particularly Hispaniola—Haiti and the Dominican Republic—where efforts are underway alongside malaria control to reach elimination by 2020. As of October 2008, the Global Programme to Eliminate LF had already prevented 6.6 million new cases in children and stopped disease progression in another 9.5 million people. Mass treatment has been rolled out in 48 of 83 endemic countries, with transmission eliminated in 21.
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Overview
Nicole Grasset was a Swiss-French medical virologist and microbiologist-epidemiologist who played a key role in the global effort to eliminate smallpox. From 1971 until the end of the World Health Organization’s smallpox eradication campaign, she served as the senior smallpox advisor for the South-East Asia Regional Office, known as SEARO. Her work was part of the broader strategy that eventually led to the last natural case of the disease and the successful eradication of smallpox worldwide.
Early life
Nicole Grasset was the daughter of a famous Swiss microbiologist and grew up in South Africa. After studying medicine, she went on to work at the Pasteur Institute in Paris. At age twenty, she wrote a "Plan of Life," which served as her life's mission statement and outlined many of the goals she would later achieve.
Eradication of smallpox
Nicole Grasset served as SEARO's principal smallpox adviser through the final stages of eradication in India and Nepal. She had previously worked as a Red Cross adviser in Biafra during the Nigerian civil war, where she provided vaccination and medical care. In her role, she coordinated efforts among SEARO states, gathered information, and helped shape policies. The eradication unit formed teams of international and Indian workers to track cases and implement containment strategies. Grasset was known for her leadership and strong personality; D.A. Henderson, who led the WHO eradication unit, described her as an "energetic, determined, charismatic leader." Aside from nursing staff, she was the only woman in the regional office. In 1977, the final smallpox case was reported in Somalia, marking the successful end of the global campaign.
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Overview
John Michael Lane, an American epidemiologist, led a critical global effort against smallpox between 1973 and 1981. He held a key position in the program aimed at eliminating the disease worldwide. His work was central to the success that culminated in the eradication of smallpox by 1977.
Early life
John Michael Lane, born February 14, 1936, in Boston, Massachusetts, was the son of Eileen O'Connor and Alfred Baker Lewis. His mother served on the national board of the YWCA and worked as a director of Planned Parenthood, while his father provided pro bono legal services for the early NAACP and later became treasurer of the organization. Lane grew up with two brothers, a half-brother, and two half-sisters. When he was six, his family relocated to Greenwich, Connecticut, where he attended the private Brunswick School. He earned a bachelor’s degree from Yale in 1957, a medical degree from Harvard in 1961, and a public health epidemiology degree from the University of California, Berkeley, in 1967. His internship was completed at Bellevue Hospital in New York.
Career
J. Michael Lane began his career as an epidemiologist with the CDC’s Epidemic Intelligence Service in 1963, working in the smallpox and other infectious diseases division. He traveled to countries like Pakistan, India, Bangladesh, and Indonesia to lead vaccination efforts. In 1973, he became director of the Global Smallpox Eradication program, serving until 1981. He oversaw the final eradication of the disease in 1977, with the last case reported in Somalia. Speaking later, Lane described how volunteers helped administer vaccines and how cooperation with local leaders was key. He also highlighted the shift from mass to ring vaccination, focusing on surveillance and containment. After the program, he remained at the CDC through 1987, then taught at Emory University and the Australian National University, helping create field epidemiology training programs. In the early 2000s, Lane advocated for destroying remaining smallpox vaccine stocks, citing bio-terrorism risks.
Personal life
J. Michael Lane married Carolina Hernandez in 1969. They divorced in 1998, and that same year he wed Lila Elizabeth Summer. He loved the outdoors, spending time bird-watching, trekking, and scuba diving. When he was seventy-nine, he finished a long hike from Atlanta to Seattle. Lane passed away in 2020 at his home in Atlanta.
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