Vaccinations prevent infectious diseases by preparing the body’s immune system to recognize and fight off specific pathogens. While most modern vaccines typically result in only mild, temporary side effects, such as soreness or redness at the injection site, some historical vaccines were known to leave a more lasting physical impression. This visible sign indicated a successful immune response and protection against serious illness.
The Smallpox Vaccine
The vaccine most famously associated with leaving a distinct, permanent mark is the smallpox vaccine. Smallpox was a highly contagious and often deadly disease responsible for countless deaths throughout history. Through a global vaccination campaign in the mid-20th century, smallpox became the first human disease to be completely eradicated, with no naturally occurring cases reported since 1977.
Routine smallpox vaccination is no longer administered to the general public in most countries, including the United States, where it ceased in 1972. However, individuals who received the vaccine before this time, particularly those born before the 1970s, often bear a characteristic scar. Today, the vaccine is only given to specific populations, such as certain military personnel or laboratory workers who may be at risk of exposure.
Why the Smallpox Vaccine Leaves a Mark
The smallpox vaccine left a scar primarily because of its unique administration method and the live virus it contained. Unlike many contemporary vaccines injected deep into muscle tissue, the smallpox vaccine utilized a technique called scarification. This involved a specialized two-pronged, or bifurcated, needle. A healthcare provider would dip this needle into the vaccine solution, which contained the live vaccinia virus, a relative of the smallpox virus but far less harmful.
The bifurcated needle was then used to rapidly prick the skin’s superficial layer, the dermis, multiple times, typically 15 times, within a small circular area, usually around 5 millimeters in diameter. This process introduced the live virus directly into the skin, causing a localized infection. This controlled infection prompted the body to mount a robust immune response. The site would progress through stages, developing a red, itchy papule, then a fluid-filled vesicle, which would become a pus-filled pustule, and finally scab over. This scab would eventually fall off, revealing the characteristic scar.
Characteristics of the Scar
The smallpox vaccine scar is quite distinctive. It typically manifests as a small, round or oval-shaped mark. The scar is often depressed or pitted, appearing slightly lower than the surrounding skin. Some scars may also have irregular edges or a somewhat star-shaped pattern, reflecting the multiple punctures made during vaccination.
The size of these scars commonly ranges from about 5 to 10 millimeters in diameter, often compared to a pencil eraser or a dime. This permanent mark is most frequently found on the upper arm or shoulder, the usual site of vaccination. The presence of this scar served as visible proof that an individual had been successfully vaccinated and had developed immunity to smallpox.
Other Vaccines and Skin Marks
While the smallpox vaccine is most well-known for leaving a distinct, permanent scar, another vaccine that can sometimes result in a skin mark is the Bacille Calmette-Guérin (BCG) vaccine. This vaccine protects against tuberculosis (TB) and is routinely administered in many parts of the world where TB is prevalent, though it is not common in the United States. The BCG vaccine can cause a localized reaction that leads to a blister, which then heals to form a small, often flat scar or discoloration.
The BCG scar typically differs from the smallpox scar; while smallpox scars are usually depressed, BCG scars can sometimes be raised and slightly rounded. It is important to distinguish these true scars from temporary reactions that can occur with almost any vaccine. Common injection site reactions, such as mild redness, swelling, or tenderness, are normal and resolve within a few days, leaving no lasting mark. These fleeting responses are signs that the body is initiating its immune defense.