I have a vivid memory of noticing a distinctive

I have a vivid memory of noticing a distinctive scar on my mother’s arm when I was a child. It sits high up, near her shoulder, and looks like a ring of small indentations in the skin surrounding one larger indentation.

Don’t ask me why it caught my attention so many years ago—I don’t remember. I only recall that it happened, but, as often occurs, I somehow forgot about its existence in the years that followed.

Of course, I never forgot that the scar was there (it’s still in exactly the same place, of course), but I forgot that at one time I’d been curious about what had caused it. Maybe I asked my mom once, and she explained—but if she did, I’ve forgotten that too.

That continued until a few summers ago, when I helped an elderly woman off a train and happened to see the very same scar, in the very same spot, that my mother has. Needless to say, my interest was piqued—but with the train about to depart for my stop, I couldn’t exactly ask her where it came from.

Instead, I called my mom, and she told me that she had actually explained it to me more than once—apparently my brain didn’t deem the answer important enough to remember—and that her scar was from the famous smallpox vaccine.

Smallpox was a viral, contagious disease that once terrorized us humans. It caused severe skin rash and fever, and at the height of outbreaks in the 20th century, according to the U.S. Centers for Disease Control and Prevention (CDC), about three out of ten victims died. Many others were left disfigured.

Thanks to the successful and widespread use of the smallpox vaccine, the virus was declared “eradicated” in the United States in 1952. In fact, routine smallpox vaccinations were discontinued in 1972.

Until the early 1970s, however, all children were vaccinated against smallpox, and the shots left a very distinctive mark. Think of it as the very first vaccine “passport,” if you like: a scar that told everyone you’d been successfully immunized against smallpox.

And yes, you guessed it—that’s the exact scar my mother bears (as do virtually everyone in her age group).

Why does the smallpox vaccine leave a scar?
The smallpox vaccine leaves a scar because of the body’s healing process. The vaccine was administered quite differently from most modern vaccines, using a special bifurcated (two-pronged) needle.

The person giving the shot made several punctures in the skin (rather than a single injection, as is common today) to deliver the vaccine into the dermis (the layer beneath the epidermis).

The live virus in the vaccine began to replicate, causing round papules to form. These papules then turned into vesicles (small fluid‑filled blisters), which eventually burst and crusted over.

The result was the notorious scar we’ve been talking about.

Are you old enough to have a smallpox vaccine scar? Let us know in the comments!