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Types of Vaccines

Active Immunization

Passive Immunization

Live Vaccines

Live vaccines are prepared from live organisms. These organisms are passed through chick embryos or other such media repeatedly till they lose their capacity to induce the disease fully, but retain the capacity to trigger off the defence mechanism. Live vaccines are usually more potent than inactivated vaccines. They multiply within the host and produce more antigens.

Live vaccines should not be given to people with immune deficiency or people being treated for certain chronic ailments or pregnant women (unless absolutely necessary).

Live virus vaccines are used for tuberculosis ( BCG), measles and polio. Usually one dose of live vaccine is enough for immunity. Some, as in the case of polio, need more. These should be spaced out. Effective storage is crucial for live vaccines. Do not receive vaccination from a centre that you suspect has poor storage facility.



Inactivated or Killed Vaccine

Certain organisms when killed by heat or chemicals and then introduced into the body induce immunity. Killed vaccines are not as effective as live vaccines. For instance the pertussis vaccine, after three doses is about 80% effective in the first three years and after 12 years not at all. Inactivated vaccines may require two or three doses. These are administered by injections.

Diphtheria, pertussis, tetanus, cholera, rabies, and hepatitis B are some diseases that are combated with killed vaccines.

Toxoids

Certain organisms when killed by heat or chemicals and then introduced into the body induce immunity. Killed vaccines are not as effective as live vaccines. For instance the pertussis vaccine, after three doses is about 80% effective in the first three years and after 12 years not at all. Inactivated vaccines may require two or three doses. These are administered by injections.

Cellular fractions

Some vaccines are prepared from fractions of the cell. The meningococcal vaccine is produced from the polysaccharide antigen on the cell wall. These vaccines are safe and effective but for a limited duration.

Combination Vaccines

This is a mix of two or more types of vaccines. This enables easier administration, reduces cost and avoids repeated contact with the patient. DPT (Diphtheria, Pertussis and Tetanus) vaccine is given in a single shot. Some vaccines combine two strains of the same species. Polio and influenza vaccines are prepared this way.

Immunoglobulins

Immunoglobulins are specific protein substances that are produced by certain cells in the body to help in fighting infection. They are also referred to as antibodies and are a vital part of the body's defence mechanism. Immunoglobulins are of five different types - Immunoglobulin G, A, M, D and E. These are classified based upon the speed with which they are formed in response to the infection, as well as their mechanism and site of action. The invading organisms or vaccines promote the production of immunoglobulins (antibodies) against that particular disease-causing organism which is then destroyed. The body also retains in its memory the template of the disease-causing organism so that the next time it attacks, the antibodies are quick to counter any threat to the body and the person does not develop the disease.

Antisera, antitoxins

Materials prepared in animals are called antisera. Since human immunoglobulin preparations are not available for all diseases, we rely on antitoxins produced from animal sources. These are used to fight tetanus, diphtheria, gas gangrene, snakebite and botulism. Antisera can produce serum sickness due to the recipient's sensitivity. So, today the preference is toward immunoglobulins.

Some Processes associated with preparation of Vaccines

Attenuation

To "attenuate" is to weaken a live micro-organism by ageing it or altering its growth conditions. This is accomplished by serial passage, that is, passing the live micro-organism through animal tissue several times to reduce its potency. For example, measles virus is passed through chick embryos, poliovirus through monkey kidneys, and the rubella virus through human diploid cells - the dissected organs of an aborted foetus.

Vaccines made in this way are often the most successful vaccines, probably because they multiply in the body thereby causing a large immune response. However, these live, attenuated vaccines also carry the greatest risk because they can mutate back to the virulent form at any time.

Detoxification

Some vaccines are made from toxins. In these cases, the toxin is often treated with aluminium or adsorbed onto aluminium salts to decrease the toxin's harmful effects. After the treatment, the toxin is called a "toxoid". Examples of toxoids are the diphtheria and the tetanus vaccines. Vaccines made from toxoids often induce low-level immune responses and are therefore sometimes administered with an "adjuvant", an agent that increases the immune response. For example, the diphtheria and tetanus vaccines are often combined with the pertussis vaccine and administered together as a DPT vaccination. The pertussis acts as an adjuvant in this vaccine.

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