I have a vivid memory from my childhood of noticing a distinct scar on my mother’s upper arm. It’s located high on her arm, near her shoulder, and takes on the appearance of a ring of small indentations circling a larger, deeper one. For some reason, that scar captured my attention back then. I can’t say exactly why I found it so fascinating—it’s one of those childhood curiosities that just sticks with you for no apparent reason. What I do remember is that I was intrigued by it, though over the years, like many things from childhood, I forgot about it.

Well, to be more accurate, I didn’t forget that it existed. After all, it’s still there, in the same spot it’s always been. But I did forget how curious I had once been about it. Maybe I even asked my mother what caused it when I was younger, and maybe she told me. If she did, that memory slipped away with time, along with the mystery that once surrounded the scar. Life moves on, and so do our minds.

Years later, however, that old curiosity was rekindled in the most unexpected way. One summer, while helping an elderly woman step off a train, I noticed a scar on her upper arm—almost identical to my mother’s. Same spot, same ring-like shape. It was like a moment from the past flashing back into focus. My curiosity was instantly reignited. But with the train about to depart for my destination, I didn’t have the chance to ask her about the mark. Still, the sight of it gnawed at me.

As soon as I could, I called my mom and told her about what I had seen. That’s when she reminded me—actually, she insisted—that she had explained it to me before. Apparently, more than once. Clearly, I hadn’t thought the explanation was significant enough to retain. But now, hearing it again as an adult, I found it genuinely fascinating. My mother’s scar was the result of the smallpox vaccine, once a common and crucial part of childhood.

For anyone unfamiliar, smallpox was a highly contagious and deadly viral disease that plagued humanity for centuries. It caused severe fever and a characteristic skin rash, often leaving survivors with deep scars and, in some cases, blindness. According to the Centers for Disease Control and Prevention (CDC), during major outbreaks in the 20th century, smallpox had a mortality rate of around 30%. That means three out of every ten people who contracted it died. Those who survived were often permanently disfigured.

Thankfully, scientists developed a vaccine that proved effective in halting the spread of smallpox. Through widespread vaccination campaigns, smallpox was eventually eradicated in the United States. The last naturally occurring case in the U.S. was in 1949, and by 1952, the virus was declared extinct in the country. Vaccination against smallpox was no longer considered necessary, and by 1972, it was removed from routine childhood immunization schedules.

But before the 1970s, virtually every child received the smallpox vaccine, and it left behind a very noticeable scar. In a way, you could think of it as the original vaccine passport—a permanent mark that indicated you had been vaccinated and were protected from a dangerous disease. That’s the scar my mother bears, and so do many others of her generation.

So, why did the smallpox vaccine leave such a distinctive scar? The answer lies in how the vaccine was administered and how the body reacted to it. Unlike many of today’s vaccines, which are given as a single injection, the smallpox vaccine required a different technique. It was delivered using a special tool called a bifurcated needle, which had two prongs designed to puncture the skin multiple times.

The vaccine was applied to the skin’s surface, and the needle was used to make several small punctures in a small area, allowing the vaccine to reach the dermis—the layer of skin beneath the outer layer, or epidermis. This method ensured that the live virus in the vaccine could effectively trigger the immune response needed to protect the person from smallpox.

Once the vaccine was administered, a localized reaction occurred. The area where the punctures were made would develop into small bumps. These bumps eventually turned into vesicles—tiny blisters filled with fluid. Over time, the vesicles would burst, scab over, and heal, leaving behind the classic scar. It’s a visible sign of the body’s response to the vaccine and its healing process.

That’s the story behind the scar I noticed on my mother’s arm—and on the arm of the woman I helped off the train. It’s a mark of a different time, when smallpox was a very real threat and vaccination was a critical tool in the fight against it. Today, that scar serves as a reminder of how far we’ve come in medicine and public health, and the global effort that led to the eradication of one of the deadliest diseases known to humankind.

Are you old enough to have a smallpox vaccine scar? Or do you know someone who has one? Feel free to share your memories or stories in the comments. We’d love to hear your thoughts. And don’t forget to share this story so others can weigh in too!