The combined injection protects against three different diseases. Tetanus is a vaccine-preventable disease that is caused by toxins produced by bacteria found in soil worldwide. Polio is a potentially paralyzing, vaccine preventable viral infection that is transmitted through food or water contaminated by human faeces or direct contact with an infected person. Diphtheria is a bacterial infection that is spread by exhaled water droplets, especially when in close contact with local population of endemic countries.