If you close your eyes and circle one word in the newspaper, it’s probably either covid or vaccine. The reason is obvious. Covid is a new and unforeseen phenomenon, however, the second word, vaccine, has been around for a long time. Vaccines have been a part of our lives right from our birth and the reason we have escaped death so far.

Everyone reading this article probably has a distinctive, round scar on their shoulder. That is from the smallpox vaccine.

For the record, smallpox was a deadly and contagious virus and declared eradicated in 1980. It included flu-like symptoms and infected patients developed rashes on their face, arms and eventually torso. However, as there is no cure or treatment for it, vaccination is the only weapon in our arsenal that can protect us from it.

The smallpox vaccine does not contain smallpox at all. It actually contains the live form of a virus called vaccina, which is similar to smallpox but less harmful. Unlike other vaccines that contain dead or weakened forms of a virus, the smallpox vaccine contains a live virus which is why the precautions taken are more stringent for patients getting vaccinated.

The presence of vaccinia in your system triggers the body to recognize and fight the virus. Antibodies are produced that can identify the virus and fight it off. In addition to this, memory cells are produced in our body which keep a record of the harmful virus and remember it. Now, if the virus infects the body again, the memory cells will recognize it and create antibodies much faster, and protect you.

But why does the smallpox vaccine leave a scar while polio and covid vaccines or even tetanus injections leave no trace behind?

Regular vaccines involve a single needle point shot to the arm. However, the smallpox vaccine is delivered using a two-pronged needle, i.e., two points of puncture. Additionally, the skin is punctured multiple times to deliver the vaccine as opposed to the single shot those other injections need.

The vaccine reaches the dermal layer of the skin and here, it begins to multiply. This causes a small bulge known as papulae, on the skin. The papulae goes on to develop into a vesicle, which is a fluid filled blister. With time, this blister will dry out and become a scab. This signifies that the vaccination has been successful.

The scar on our shoulder is the remnant of that blister. This scar was also used in some countries to conveniently check whether immigrants were vaccinated or not.