By Richard Rupp and Bridget Hawkins 

Dear VaccineSmarts,
I’m remodeling my house and stepped on a nail in the floorboard. The nail wasn’t rusty.
I went to my doctor to get a tetanus shot and he said I probably did not need one but gave me the shot anyway.
What did his comment mean?


Dear Carl,

Contrary to common belief, rust does not cause tetanus. Tetanus is caused by a bacterium that is in the feces of many animals such as birds, dogs, cats, rats and cattle.

Feces frequently contaminate the soil and other things that are outdoors.

Rust is just a marker that something has been outdoors and has a good chance of being contaminated.

Tetanus rarely develops with superficial scrapes because the wound is open to the air and this high oxygen environment makes it difficult for the bacterium to grow.

Nails are the perfect way to introduce tetanus because the nail puncture places the bacterium deep into the body, away from open air.

This low-oxygen environment along with the damaged tissue encourages the bacterium to grow.

The growing bacterium produces a toxin that causes painful muscle spasms.

The spasms usually start in the jaw muscles then spread to other muscles of the body, making it difficult to swallow and even breathe.

If left untreated, about three quarters of the affected die. Treatment includes the use of antitoxin, antibiotics, muscle relaxants and ventilators.

On average, there are only about 30 cases of tetanus each year in the United States. About 1 in every 10 cases results in death.

The number of cases has decreased by more than 95 percent since 1947. The decrease is because of changes in wound management and widespread vaccination.

In this country, the primary risk factor for tetanus is not being vaccinated or not current with vaccination.

Other risk factors include being 65 years or older, having diabetes or being an intravenous drug user.

In this country, infants receive the primary series of tetanus vaccines at 2, 4 and 6 months old.

Children get booster shots after their first birthday and again at 4 to 6 years old.

Adolescents receive their booster dose at 11 to 12 years of age. After that, everyone should get a booster every 10 years.

Your physician’s comment about not needing the vaccine probably reflects his belief that contamination of the nail was unlikely.

The nail had been uncovered only a brief amount of time and should not have been exposed to animal feces or soil.

If it had been more than five years since your last tetanus vaccine, it was a good idea to be vaccinated. Better safe than sorry.

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