What is the main purpose of vaccination?

The main purpose of vaccination is to build immunity against pathogens. Vaccines work by exposing the immune system to a harmless component or a weakened form of the pathogen, which triggers the body's immune response. This response includes the production of antibodies and the activation of immune cells that can recognize and combat the actual pathogen if the person is exposed to it in the future.

Vaccination does not aim to treat diseases after an infection has already occurred, which is why this option is not correct. Additionally, while vaccines can help reduce susceptibility to infections that might indirectly relate to other issues such as food allergies, that is not their main purpose. Vaccines also do not eliminate all pathogens from the body; instead, they prepare the immune system to fight specific pathogens effectively when they are encountered. Therefore, building immunity is the fundamental goal of vaccination, making it the correct answer.