Many people have a small round scar on their upper left arm, usually from childhood smallpox or BCG vaccinations. The mark forms when the vaccine creates a blister that heals into a permanent scar, a common sign of immunization in past decades.

Smallpox was once among humanity’s most feared diseases. Caused by the variola virus, smallpox could erupt in mild or severe forms, but its most virulent strain had a mortality rate around 30 percent. Survivors often endured horrifying symptoms — high fever, severe fatigue, and a blistering, pus-filled rash that covered large areas of the body. The rash left deep, pock-like scars, frequently disfiguring faces and bodies for life. In addition to disfigurement, some survivors suffered blindness or other long-term complications. Because smallpox spread easily and could wipe out entire communities, it posed an existential threat for centuries across continents.

Faced with such a devastating illness, the development of an effective vaccine became one of the most urgent and consequential priorities in medical history.

The roots of smallpox vaccination go back to the late 18th century, when English physician Edward Jenner observed that milkmaids previously infected with cowpox rarely contracted smallpox. In 1796, he demonstrated that inoculation with material from cowpox (or related viruses) offered protection against variola. Over time, the vaccine strain changed: a related virus known as vaccinia virus — harmless relative of variola — became the standard agent used in smallpox immunization campaigns.

A major innovation came in the 1960s: the invention of the bifurcated needle, with two prongs, optimized for smallpox vaccination. This needle allowed health workers to deliver the vaccine by lightly pricking the skin multiple times — a rapid and efficient method that facilitated mass-vaccination campaigns. Beginning in 1967, under the auspices of the World Health Organization (WHO), countries around the world embarked on a coordinated eradication campaign combining widespread vaccination and vigilant surveillance.

The efforts proved successful: by 1977, the last naturally occurring case of smallpox was recorded. In 1980, the WHO officially declared smallpox eradicated — marking the first and only time humanity has eliminated a major infectious disease globally through vaccination.

Unlike most modern vaccines, the smallpox vaccine was not delivered via a deep injection into muscle or subcutaneous tissue. Instead, it was administered into the skin — specifically the dermis — using multiple shallow punctures from the two-pronged bifurcated needle. Because the vaccine used live vaccinia virus, the body mounted a localized immune response. Within a few days, a red bump formed at the site, quickly progressing to a fluid-filled blister, then a pustule, and eventually forming a scab.

Over the course of two to three weeks, as the scab dried and fell off, the healed area was left with a small, circular, crater-like mark — the classic “smallpox vaccine scar.” The scar’s appearance varies: for many people it’s a small round indentation a few millimeters across (often compared to the size of a pencil eraser), while in others it may be larger or more pronounced depending on their skin’s response and healing.

In historical vaccination campaigns, the upper left arm was typically used — both for convenience and consistency. That’s why, today, when someone sees an older person with a round scar on their upper arm, it’s often recognized (whether explicitly or subconsciously) as the mark of smallpox vaccination.

For decades, the smallpox vaccine scar served not just as a physical mark, but as a public sign of immunity and survival. During smallpox outbreaks — especially in the late 19th and early 20th centuries — authorities sometimes required proof of vaccination before allowing travel, school enrollment, employment, or attendance at public events. In effect, the scar functioned as an early “vaccine passport.”

Because mass vaccination campaigns reached nearly every corner of the globe, millions of people across continents — from North America to Africa, Europe to Asia — ended up with the distinctive round scar. For many survivors of the smallpox era, the scar came to symbolize more than mere protection: it was a visible testament to having lived through a time when the disease was a real and present threat worldwide. As some have described it, the scar became a “badge of honour” — proof that the individual had done their part in conquering one of humanity’s greatest scourges.

Because of the global eradication of smallpox, routine vaccination for the general public stopped decades ago. In the United States, routine smallpox vaccinations ended around 1972. The last natural case occurred in 1977; by 1980 the disease was declared eradicated. As a result, people born after the early 1970s — especially those born in the 1980s and later — are unlikely ever to have received the vaccine, and thus do not carry the scar.

Today, only select groups receive smallpox (or related orthopoxvirus) vaccines — for instance, certain laboratory workers, some military personnel, or public-health responders who may deal with biothreats. The vaccine used in such cases may still produce the classic scar (if a live replicating vaccinia formulation is used, as with older smallpox vaccines like ACAM2000).

Because of this history, the smallpox-vaccine scar has become something of a living relic — a physical reminder of a world before eradication, and proof of one of medicine’s greatest triumphs. When younger people see older generations with that scar, it can prompt curiosity, historical reflection, or simply recognition of how far public health has come.

The story of smallpox — from ancient scourge to global eradication — is among humanity’s greatest achievements in medicine and public health. The vaccine, based on the vaccinia virus, succeeded where other interventions failed, turning a once-deadly disease into a memory. The smallpox vaccine scar, then, is more than just a mark on the skin: it is a symbol of survival, science, and collective action.

Each scar identifies someone who, or whose ancestors, lived through an era when smallpox was a constant threat — a world where outbreaks could decimate communities, leave survivors permanently scarred or blind, and cause widespread mourning and fear. From the removal of natural smallpox transmission to the end of routine vaccination, the scar stands as a silent, enduring testament to the power of vaccines.

Even today — as the disease is safely confined to secure laboratories — the scars remind us of both the fragility and resilience of human societies. They show what determined global cooperation, medical ingenuity, and public-health commitment can achieve. As new generations grow up without ever seeing smallpox, the scar remains a meaningful historical marker — a reminder that through science, solidarity, and persistence, humanity can overcome even the most terrifying diseases.