To induce an immune response that would shield humans from the dangerous Variola virus that caused smallpox, live Vaccinia virus was utilized.
Blisters develop at the injection site after receiving a shot. Within a few weeks, the blisters heal and form a crust.

The final end has a circular scar. Each time the needle pierced the skin, a tiny amount of the vaccine was applied, and blisters developed. The scars are so evident because of this.
The area where the shot was administered expands slightly immediately and over the following 6 to 8 hours.

After that, the edema goes away and the injection site seems normal. After 6 to 8 weeks, a lump that resembles a mosquito bite returns.

It begins to grow and develop into a tumor. It eventually cracks open, starts to seep fluid, and develops into an ulcer.