Tetanus is caused by a germ that enters the body through a cut or wound.
Diphtheria spreads when germs pass from an infected person to the nose or throat of others.
Because of the vaccination, there are many fewer cases of these diseases. There would be many more cases if we stopped vaccinating people. Td is made for people 7 years of age and older. After a person gets the third dose, a Td dose is needed every 10 years all through life. Other vaccines may be given at the same time as Td.