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Vaccines

Vaccine is a biological substance designed to produce specific protection against a given disease. Vaccines can be either prepared from live organisms or dead organisms.

Live vaccines
Live vaccines are prepared from live (generally attenuated) organisms. The organisms are processed in a laboratory such that they lose their ability to produce yet be able to produce an immune response.

Are there any contraindications to live vaccination?
Live vaccines should not be administered to persons whose immune system is compromised. Such patients include people who have cancers or are being treated with anticancer agents., transplant patients, patients taking steroids etc. In addition pregnant patients should not be given live vaccines as there is a risk of harm to the baby. When two live vaccines are required they should be given either simultaneously different sites or with an interval of at least 3 weeks.

Live vaccines must be properly stored to retain effectiveness. Inactivated or killed vaccines: eg hepatitis, cholera, typhoid and whooping cough. Toxoids: A toxoid is a vaccine which is prepared from the toxins of organisms. They undergo purification before use. eg tetanus. The toxins produced by these organisms are detoxicated and used in the preparation of vaccines. e.g. Diphtheria Tetanus. In order to reduce costs, the ease of administering the vaccine many of the vaccines are combined. e.g. are DPT (Diphteria–pertussis–tetanus) DT (Diphtheria–tetanus), MMR (Measles, mumps and rubella). Many times substances are added to vaccines( called adjuvants) to enhance their effectiveness. Substances added are usually aluminum compounds.

Storage of vaccines
Effectiveness of vaccines can be lost if they are not stored appropriately. A system of cold storage is used from the time the vaccine is manufactured until it is used. Among the vaccines, polio is the most sensitive to heat, requiring storage at–200 c. Vaccines which must be stored in the freezer compartment are: Polio, measles and BCG. Vaccines which must be stored in the refrigerator but not in the freezer compartment are: typhoid, DPT, tetanus toxoid and diluents. Vaccine must be protected from sunlight and prevented from contact with antiseptic. At the health centers, most vaccines (except polio) can be stored up to 5 weeks if the refrigerator temperature is strictly kept between 4 to 8 degrees C.

Opened multi–dose vials which have not been fully used should be discarded within one hour, if no preservatives is present (most live virus vaccines) or within 3 hours, or at the end of a session when containing a preservative are used.

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