Immunization

In the medical context, immunization refers the introduction of a vaccine or similar agent for purpose of rendering a body immune to disease. Vaccines introduce a small amount of a virus (often a dead form that cannot spread) into the body, triggering the production of antibodies. The antibodies then provide protection against the real virus. Some common examples are childhood immunization to diphtheria and measles. Some diseases, such as diphtheria and smallpox, have been rendered extremely rare or completely extinct through widespread immunization through vaccination.

In the legal context, immunization refers to being made excempt from the normal legal duties or liabilities. For example, a witness can sometimes be offered immunity in exchange for testifying.

Immunisation is the process of granting immunity from something to something. This is most often used to refer to vaccination, where immunity to a disease is artificially granted by an injection of a weakened or dead strain of an antigen, or by an injection of antibodies. It can also be used legally to refer to immunity to prosecution and occasionally in other contexts e.g. immunity to certain weapons (in RPGs).

Medical immunisation can be either active or passive, and artificial or natural. Active immunity occurs when b-lymphocytes bind to an antigen, different lymphocytes have different binding sites, only some of which will allow the lymphocyte to bind to the antigen. The lymphocytes that bind will then divide, so many cells with the correct binding sites are produced, some of these, called plasma cells, produce antibodies that can bind to the antigen, others, called memory cells, stay in the bloodstream in case the antigen returns, enabling a much faster response if the antigen returns.

Passive immunity is where antibodies from another source enter the body, conferring tempory immunity to the specific disease.

Artificial immunity is man made, such as vaccinations, or injections of antibodies. Natural immunity is produced by the body, such as when an antigen enters it, or antibodies given to a baby in its mother's milk.

The word Immune is derived from the Latin meaning exempt. In the late 18th century a physician named Edward Jenner noticed that milk-maids, although frequently developed cowpox, very rarely developed smallpox. He carried out an experiment in which he injected pus from a cowpox lesion into a healthy boy. Obviously the boy developed cowpox. Jenner then injected the same boy with puss from a smallpox lesion. But the boy didn't develop smallpox. This is because the cowpox virus is very similar to the smallpox virus only it's much less harmful. As the two viruses were so similar, if the immune system could overcome the less dangerous cowpox it would be able to quickly recognise and destroy the much more threatening smallpox virus.

The body had developed cells which "remembered" cowpox-like viruses. This is how vaccination came about. Vaccination is derived from the word vacca meaning cow. Later on Louis Pasteur showed that attentuated (weakened) live viruses and heat killed bacteria can be used for vaccination against disease.

Types of Immunisation

Active. Active immunisation is termed vaccination and elicits a response from the body that provides protective immunity.
Passive. Passive Immunisation is the injection of antibodies into the body to provide short-term protection.

Vaccination is intended to provide long-term protection after its administration. So the most important quality a vaccine must have is to generate immunological memory.

• Live Attentuated e.g. Poliomyelitis, MMR, BCG and Yellow Fever
• Killed e.g. Pertussis (Whooping Cough)
• Toxoid i.e. Pathogen released toxins that have been modified. E.g. Diptheria and Tetanus
• Recombinant e.g Hepatitus B
• Congugate Capsular Polysaccharide e.g. Typhoid and Haemophilus Influenzae B (Hib)

A very important point to note is that live vaccines should never be given to immunosuppressed individuals.