Tetanus booster. Man receiving a tetanus (lockjaw) booster injection in his upper arm. This booster reinforces the tetanus vaccinations given to the patient when he was a child. Booster injections are given to adults once every ten years or after an injury. Vaccination does not give total protection against infection, but it reduces the chance of serious illness developing. Tetanus is caused by the Clostridium tetani bacterium which lives harmlessly in the soil and human intestine. It causes lockjaw after infecting a wound, causing muscle stiffness, spasms and possibly death.