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 –20 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.
The Cold Chain Equipment
All vaccines at PHC level are stored in the small deep freezer. Vaccine like TT, DPT, DT, and diluents are kept in thee basket provided with the freezer. At the time of defrosting the vaccines are shifted to the cold boxes containing required number of frozen ice packs. In the event of electric supply failure, vaccines should be transferred to ice boxes and then to alternate vaccine storage.
DO's: Keep the equipment in cool room away from direct sunlight and at least 10 cms away from the wall, keep the equipment leveled, fix the equipment through voltage stabilizer, keep the equipment locked and open only when necessary, defrost periodically, supervise the temperature record, and if vaccines are kept in cartons, make holes on the sides of the cartons for cold air circulation. DONT’s: Do not keep any object on these equipments, do not store any other drug, do not keep drinking water or food in them, do not keep more than one month’s requirements at PHC levels, and do not keep date expired vaccines.
Cold boxes are supplied to all peripheral centres. These are used mainly for transportation of the vaccine.
Vaccine carriers are used to carry small quantities of vaccines (16–20) vials for out of reach sessions. Four fully frozen ice packs are used for lining the sides, and vials of DPT, DT, TT and diluents should not be placed in direct contact with frozen ice packs. The careers should be closed tightly.
The ice packs contain water and no salt should be added to it. The water should be filled up to the level marked on the side. If there is any leakage, such ice packs should be discarded.