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.

Tetanus is found worldwide but is generally more common in countries with poor vaccination coverage. Polio is now only endemic in Afghanistan and Pakistan but it can be imported to other countries by infected individuals. Diphtheria can be found worldwide but is more common in developing countries where vaccination coverage is not as widespread.