Only one human disease has ever been fully eradicated: smallpox. The World Health Organization officially declared the world free of smallpox on May 8, 1980, making it the first and still only human infectious disease wiped out entirely through deliberate effort. A second virus, rinderpest, was declared eradicated in 2011, but it affected cattle and wildlife rather than people.
What “Eradicated” Actually Means
Eradication has a precise meaning in public health. It refers to the permanent, worldwide reduction to zero cases of infection caused by a specific agent, achieved through deliberate human effort. Once a disease is eradicated, no further vaccination or intervention is needed to keep it gone. This is a much higher bar than “elimination,” which means zero cases in a specific country or region but still requires ongoing measures to prevent the disease from returning. And it’s distinct from “extinction,” which would mean the infectious agent no longer exists anywhere, not even in a laboratory freezer. Smallpox has been eradicated but not technically made extinct.
Smallpox: The Only Human Virus Eradicated
Smallpox killed an estimated 300 million people in the 20th century alone before its eradication. The disease was caused by the variola virus and spread through close contact, producing fever and a progressive, blistering rash that left survivors permanently scarred and sometimes blind. It had no treatment. About 30% of people who caught the most severe form died.
The global campaign to eliminate it began in earnest in 1967, coordinated by the WHO. Two innovations made the campaign feasible. First, a bifurcated needle developed in 1961 was cheap, easy to use in remote field conditions, reusable up to 100 times after sterilization, and required only one-quarter of the vaccine dose previously needed. Vaccination success rates climbed to nearly 100%. Second, rather than trying to vaccinate every person on Earth, health workers adopted a strategy called “ring vaccination,” tracking down every new case and vaccinating everyone around it to cut off transmission.
The last naturally occurring case was recorded in Somalia in 1977. A global commission certified eradication in December 1979, and the World Health Assembly formally accepted it on May 8, 1980, declaring that “the world and all its peoples have won freedom from smallpox.” The total cost of the eradication effort was roughly $300 million over a decade. It now saves an estimated $1 billion per year in healthcare costs worldwide, since no country needs to vaccinate against it or treat cases.
The variola virus itself still exists. Two WHO-designated laboratories keep stocks for research: the CDC in Atlanta and the Russian State Centre for Research on Virology and Biotechnology in Koltsovo, Russia. Whether to destroy those final samples has been debated for decades but never resolved.
Rinderpest: The Only Animal Virus Eradicated
Rinderpest, sometimes called “cattle plague,” was declared eradicated on May 25, 2011. It was caused by a virus in the same family as measles and infected cattle along with more than 40 other species of hoofed animals. Outbreaks could kill 80 to 90% of affected herds, triggering famine in communities that depended on livestock. A coordinated global vaccination campaign led by the UN’s Food and Agriculture Organization ultimately drove the virus to extinction in the wild. Rinderpest is the second disease of any kind, and the only animal disease, to be eradicated.
Polio Is Close but Not There Yet
Polio is often mentioned alongside smallpox because a massive global campaign has been working toward its eradication since 1988. The effort has come remarkably close. Of the three types of wild poliovirus, type 2 was last detected in 1999 and declared eradicated in 2015. Type 3 hasn’t been seen since November 2012. That leaves only wild poliovirus type 1 still circulating, and it persists in just two countries: Afghanistan and Pakistan. As of early 2026, Pakistan had reported 26 cases and Afghanistan one case for the year.
The remaining pockets have proven extremely difficult to reach due to conflict, political instability, and pockets of vaccine refusal. Until type 1 is gone worldwide with no cases for several consecutive years, polio cannot be declared eradicated. Complicating the picture further, weakened virus from the oral polio vaccine itself can occasionally mutate and regain the ability to cause outbreaks in under-vaccinated communities, a problem that requires its own containment efforts.
Why So Few Diseases Have Been Eradicated
Eradication is exceptionally hard. A disease is only a realistic candidate if it meets several biological criteria: it must infect only humans (or have no lasting animal reservoir), there must be an effective and affordable intervention to stop transmission, and cases must be detectable before the infected person spreads it widely. Smallpox checked every box. It had no animal host, the vaccine was highly effective and heat-stable, and the visible rash made every case easy to identify and track.
Most infectious diseases fail at least one of these tests. Malaria has an insect vector that’s nearly impossible to eliminate globally. Tuberculosis can hide in the body for years without symptoms. Influenza mutates so rapidly that no single vaccine provides lasting immunity. Even measles, which has a highly effective vaccine, circulates so efficiently that a single unvaccinated pocket can reignite outbreaks.
An international task force has identified a short list of diseases considered potentially eradicable with current tools: polio, mumps, rubella, lymphatic filariasis, and cysticercosis (caused by a pork tapeworm). Each faces significant hurdles, from diagnostic limitations to a lack of data on disease burden in developing countries. None is expected to be eradicated soon. For now, smallpox stands alone as proof that it can be done.