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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.

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 already raised an immune response to the pathogen. The passive vaccine of antibodies means that the patient does not need to wait to raise their own immune response, because the antibodies that would need to be made are simply delivered themselves straight into their blood.

Immunisation attempts through vaccination have had varying degrees of success for different diseases. Smallpox is an example of eradication through vaccination, while flu is an example of management and prevention through vaccination, but not long term eradication.

There are ethical considerations surrounding vaccination. On the one hand, large scale vaccination can prevent escalation of epidemics via herd immunity. When more people are immune to a certain infectious agent, transmission from person to person becomes more difficult even when a small number of cases do occur.

Therefore, anyone getting vaccinated would want to ensure others follow suit. On the other hand, the personal decision to get vaccinated can interfere with the goal of achieving a good immunity status for a given population against an illness. Some people would be cautious to get themselves or their children vaccinated due to suspected long term side effects.

The balance of personal autonomy versus achieving greater societal goals that require everyone to synchronise in their decision making has to be accomplished.

Active immunity refers to immunity acquired as a result of an illness. This is also the type of immunity induced via vaccination, as the body is responding in the same way when it encounters the pathogenic antigen and responds appropriately.

Passive immunity is the type of immunity acquired directly via the relevant antibodies rather than by developing them afresh following disease or other ways of contacting antigens. An example is the immunity passed to a foetus via the placenta during gestation.

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