Vaccinations prevent symptoms of an illness (such as flu or rubella) from developing, by creating a primary immune response to an unharmful substance that the body identifies as a pathogen. This could be an antigen, or the pathogen itself – dead or otherwise modified to prevent disease. Some vaccines are really successful and have prevented many diseases so far, yet the flu vaccine remains a challenge due to the above points. The virus changes its antigens, and there is great variation to start off with.
Booster vaccination is administered (e.g. every 10 years for tetanus) to make up for decreasing immunity over time due to memory cells dying. It boosts the immune response back to levels that confer protection against the disease.
Our natural immunity does not cover certain pathogens such as the flu virus. Vaccination attempts to induce artificial immunity which is an add-on to our natural immunity, by adding an artificially triggered response specific to a new pathogen that we did not have innately.
In the case of rabies, a vaccine is given containing antibodies in order to act as an emergency, passive treatment. Normally, the rabies vaccine would be given preventively to avoid getting the disease, but if someone is likely to have already got infected without prior vaccination, the administration of ready antibodies into their blood can help tackle the illness in its tracks. The antibodies would be obtained from someone else’s blood who has…