Vaccine Smarts
By Dr. Richard Rupp and Bridget Hawkins, Ph.D. 

Dear VaccineSmarts,
I have a scar on my upper arm. I think it is ugly and wish it wasn’t there.
I was born in Mexico. My mother has a similar scar, but my younger brothers and sister who were born in Texas do not.
My mother tells me the scar is from a vaccine but she is not sure which one.
My high school biology teacher thinks it may be from the Smallpox vaccine.
Will you tell me which vaccine and why my siblings do not have scars?


Dear Maria,

You are very observant and have done most of the detective work. Both the Smallpox and BCG vaccines leave a scar on the upper arm.

Your scar is from the BCG vaccine. We will explain how we know this and we will explain the BCG vaccine.

Smallpox is a horrible disease that caused a scarring rash and killed many people.

The World Health Organization organized a vaccination campaign that eliminated Smallpox from the world.

The last natural case of Smallpox occurred in Somalia in 1977, and the disease was officially declared eradicated in 1980.

Many older people have a scar from the Smallpox vaccine, but you are not old enough to have received this vaccine.

Routine smallpox vaccination stopped in 1972 in the U.S. All countries had quit routine vaccination by 1986.

So, that leaves the BCG vaccine. BCG stands for Bacillus Calmette-Guérin. The BCG vaccine is used to protect people from human tuberculosis.

Interestingly, the BCG vaccine strain was developed from the bacteria that cause tuberculosis in cows. People can catch cow TB by being in close contact with cows or by drinking infected milk.

People will not develop cow TB from the BCG vaccine strain because it is attenuated. Attenuated means it is a weak form without the ability to cause disease. It is better adapted for living in culture dishes than in a living body.

People develop an immune response to the BCG vaccine that provides some protection against severe cases of human TB.

The BCG vaccine also makes people have a positive skin test for TB. There is not any easy way to tell if a person who has a positive TB skin test has been exposed to TB or if it is a reaction to the BCG vaccine.

Because of these issues, the BCG vaccine is routinely used only in countries with high rates of TB. The U.S. has a low rate of TB, whereas it is much higher in Mexico.

As a result, the BCG vaccine is not recommended for routine use in the U.S., whereas it is in Mexico.

The BCG vaccine is given just under the skin. Two to four weeks later, a pustule occurs at the site. The pustule might open and drain.

The size of the scar depends on the amount of inflammation caused by the person’s immune response and the person’s healing ability. People with a tendency to scar or form keloids tend to be those with the most obvious scars.

We are impressed with your high level of curiosity. Perhaps you should consider a career in science.

Dr. Richard Rupp is a pediatrician and member of UTMB’s Sealy Center for Vaccine Development. Bridget Hawkins, Ph.D., is the assistant director of the Sealy Center for Vaccine Development. This column is supported by a UTMB President’s Cabinet Award to provide information about vaccines. Visit for more information.